Delay-Tolerant Networking E.J. Birrane
Internet-Draft B. Sipos
Intended status: Standards Track J. Ethier
Expires: 4 January 2025 JHU/APL
3 July 2024
DTNMA Application Management Model (AMM) and Data Models
draft-ietf-dtn-amm-00
Abstract
This document defines a data model that captures the information
necessary to asynchronously manage applications within the Delay-
Tolerant Networking Management Architecture (DTNMA). This model
provides a set of common type definitions, data structures, and a
template for publishing standardized representations of model
elements.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 4 January 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Data Modeling Concept of Operations . . . . . . . . . . . . . 6
2.1. Values and Value-Producing Objects . . . . . . . . . . . 8
2.2. Agent Processing . . . . . . . . . . . . . . . . . . . . 10
2.3. Agent-Manager Messaging . . . . . . . . . . . . . . . . . 11
3. Application Management Model (AMM) . . . . . . . . . . . . . 12
3.1. AMM Values . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.1. Literal Values . . . . . . . . . . . . . . . . . . . 12
3.1.2. Object Reference Values . . . . . . . . . . . . . . . 13
3.1.3. The Application Resource Identifier (ARI) . . . . . . 15
3.2. Built-In Types . . . . . . . . . . . . . . . . . . . . . 15
3.2.1. Simple Types . . . . . . . . . . . . . . . . . . . . 16
3.2.2. Containers . . . . . . . . . . . . . . . . . . . . . 19
3.2.3. Object Reference Types . . . . . . . . . . . . . . . 21
3.2.4. Value-Class Types . . . . . . . . . . . . . . . . . . 22
3.2.5. Custom Types . . . . . . . . . . . . . . . . . . . . 22
3.3. Semantic Types . . . . . . . . . . . . . . . . . . . . . 23
3.3.1. Named Type Use . . . . . . . . . . . . . . . . . . . 23
3.3.2. Uniform List . . . . . . . . . . . . . . . . . . . . 24
3.3.3. Diverse List . . . . . . . . . . . . . . . . . . . . 24
3.3.4. Uniform Map . . . . . . . . . . . . . . . . . . . . . 24
3.3.5. Table Template . . . . . . . . . . . . . . . . . . . 25
3.3.6. Type Union . . . . . . . . . . . . . . . . . . . . . 25
3.3.7. Sequence . . . . . . . . . . . . . . . . . . . . . . 25
3.4. AMM Object Types . . . . . . . . . . . . . . . . . . . . 25
3.4.1. Common Object Fields . . . . . . . . . . . . . . . . 26
3.4.2. Semantic Type Definition (TYPEDEF) . . . . . . . . . 27
3.4.3. Externally Defined Data (EDD) . . . . . . . . . . . . 28
3.4.4. Constant (CONST) . . . . . . . . . . . . . . . . . . 29
3.4.5. Control (CTRL) . . . . . . . . . . . . . . . . . . . 29
3.4.6. Operator (OPER) . . . . . . . . . . . . . . . . . . . 30
3.4.7. State-Based Rule (SBR) . . . . . . . . . . . . . . . 31
3.4.8. Time-Based Rule (TBR) . . . . . . . . . . . . . . . . 32
3.4.9. Variable (VAR) . . . . . . . . . . . . . . . . . . . 33
4. Application Data Models (ADMs) . . . . . . . . . . . . . . . 35
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4.1. ADM Definitions . . . . . . . . . . . . . . . . . . . . . 35
4.1.1. ADM Metadata . . . . . . . . . . . . . . . . . . . . 35
4.1.2. Features and Conformance . . . . . . . . . . . . . . 36
4.2. Contents of a DTNMA ADM . . . . . . . . . . . . . . . . . 36
4.2.1. Simple Semantic Types . . . . . . . . . . . . . . . . 37
4.2.2. Type Unions . . . . . . . . . . . . . . . . . . . . . 37
4.2.3. Expression (EXPR) . . . . . . . . . . . . . . . . . . 38
4.2.4. Macro (MAC) . . . . . . . . . . . . . . . . . . . . . 38
4.2.5. Report Template (RPTT) . . . . . . . . . . . . . . . 39
4.2.6. Execution Target Type . . . . . . . . . . . . . . . . 39
4.2.7. Evaluation Target Type . . . . . . . . . . . . . . . 39
4.3. Contents of an Agent ADM . . . . . . . . . . . . . . . . 40
4.3.1. Agent State Introspection . . . . . . . . . . . . . . 40
4.3.2. Macro Helper Controls . . . . . . . . . . . . . . . . 40
4.3.3. Basic Operators . . . . . . . . . . . . . . . . . . . 41
5. Operational Data Models (ODMs) . . . . . . . . . . . . . . . 41
6. Processing Activities . . . . . . . . . . . . . . . . . . . . 42
6.1. Agent Initialization . . . . . . . . . . . . . . . . . . 42
6.2. ARI Resolving . . . . . . . . . . . . . . . . . . . . . . 43
6.3. Dereferencing . . . . . . . . . . . . . . . . . . . . . . 43
6.4. Parameter Handling . . . . . . . . . . . . . . . . . . . 44
6.5. Value Production . . . . . . . . . . . . . . . . . . . . 45
6.5.1. CONST and VAR Objects . . . . . . . . . . . . . . . . 45
6.5.2. EDD Objects . . . . . . . . . . . . . . . . . . . . . 46
6.6. Execution . . . . . . . . . . . . . . . . . . . . . . . . 47
6.6.1. Expanded MAC Values . . . . . . . . . . . . . . . . . 48
6.6.2. CTRL Objects . . . . . . . . . . . . . . . . . . . . 48
6.7. Evaluation . . . . . . . . . . . . . . . . . . . . . . . 49
6.7.1. Expanded EXPR Values . . . . . . . . . . . . . . . . 50
6.7.2. OPER Objects . . . . . . . . . . . . . . . . . . . . 51
6.7.3. TYPEDEF Objects . . . . . . . . . . . . . . . . . . . 51
6.7.4. ARITYPE Values . . . . . . . . . . . . . . . . . . . 52
6.8. Reporting . . . . . . . . . . . . . . . . . . . . . . . . 52
6.8.1. RPTT Values . . . . . . . . . . . . . . . . . . . . . 52
6.8.2. Value-Producing Objects . . . . . . . . . . . . . . . 53
6.9. Agent-Manager Message Handling . . . . . . . . . . . . . 53
6.9.1. Execution-Set Aggregation . . . . . . . . . . . . . . 53
6.9.2. Execution-Set Processing . . . . . . . . . . . . . . 54
6.9.3. Reporting-Set Aggregation . . . . . . . . . . . . . . 54
6.9.4. Reporting-Set Processing . . . . . . . . . . . . . . 54
6.10. Type Matching . . . . . . . . . . . . . . . . . . . . . . 54
6.10.1. Built-In Types . . . . . . . . . . . . . . . . . . . 54
6.10.2. Semantic Types . . . . . . . . . . . . . . . . . . . 56
6.11. Type Conversion . . . . . . . . . . . . . . . . . . . . . 57
6.11.1. BOOL Type . . . . . . . . . . . . . . . . . . . . . 57
6.11.2. NUMERIC Types . . . . . . . . . . . . . . . . . . . 58
6.11.3. Semantic Types . . . . . . . . . . . . . . . . . . . 59
6.12. Translating ARIs and Semantic Types . . . . . . . . . . . 61
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7. ADM Author Considerations . . . . . . . . . . . . . . . . . . 62
7.1. CTRL Definitions Need to Consider Idempotency . . . . . . 62
7.2. EDD Definitions Need to Consider Nilpotency . . . . . . . 62
7.3. Use Parameters for Dynamic Information . . . . . . . . . 62
7.4. Do Not Use Parameters for Static Information . . . . . . 63
7.5. Use Tables for Related Data . . . . . . . . . . . . . . . 63
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 64
8.1. DTN Management Architecture Parameters . . . . . . . . . 64
9. Security Considerations . . . . . . . . . . . . . . . . . . . 64
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 64
10.1. Normative References . . . . . . . . . . . . . . . . . . 64
10.2. Informative References . . . . . . . . . . . . . . . . . 65
Appendix A. Access Control Lists . . . . . . . . . . . . . . . . 66
A.1. Tags . . . . . . . . . . . . . . . . . . . . . . . . . . 67
A.2. Groups . . . . . . . . . . . . . . . . . . . . . . . . . 67
A.2.1. Associations . . . . . . . . . . . . . . . . . . . . 67
A.2.2. Permissions . . . . . . . . . . . . . . . . . . . . . 68
A.2.3. Execution Context . . . . . . . . . . . . . . . . . . 69
A.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 69
A.3.1. Dereferencing . . . . . . . . . . . . . . . . . . . . 69
A.3.2. Parameter Handling . . . . . . . . . . . . . . . . . 69
A.3.3. Value Production, Execution, and Evaluation . . . . . 69
A.3.4. Reporting . . . . . . . . . . . . . . . . . . . . . . 70
A.4. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 70
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 70
1. Introduction
The Delay-Tolerant Networking Management Architecture (DTNMA)
[I-D.ietf-dtn-dtnma] defines a concept for the open-loop control of
applications (and protocols) in situations where timely, highly-
available connections cannot exist among managing and managed nodes
in a network. While the DTNMA provides a conceptual information
model, it does not include details necessary to produce interoperable
data models.
1.1. Scope
This document defines a two-level data model suitable for managing
applications in accordance with the DTNMA. The two levels of model
are:
1. A meta-model for the DTNMA, called the Application Management
Model (AMM), which defines the object structures and literal-
value types used in the DTNMA in a concrete way.
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2. An object model, based on the AMM meta-model, which is used in
static Application Data Models (ADMs) and dynamic Operational
Data Models (ODMs) as instances of the AMM within an Agent.
This document does not define any specific encodings of AMM values or
of ADM or ODM contents. In order to communicate data models and
values between DTNMA Agents and Managers in a network, they must be
encoded for transmission. Any such encoding scheme is outside of the
scope of this document. Generally, the encoding of the model is a
separate concern from the specification of data within the model.
Because different networks may use different encodings for data,
mandating an encoding format would require incompatible networks to
encapsulate data in ways that could introduce inefficiency and
obfuscation. It is envisioned that different networks would be able
to encode values in their native encodings such that the translation
of ADM data from one encoding to another can be completed using
mechanical action taken at network borders.
Since the specification does not mandate an encoding format, the AMM
and ADM must provide enough information to make encoding (and
translating from one encoding to another) an unambiguous process.
Therefore, where necessary, this document provides identification,
enumeration and other schemes that ensure ADMs contain enough
information to prevent ambiguities caused by different encoding
schemes.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The terms "Actor", "Agent", "Externally Defined Data", "Variable",
"Constant", Control", "Literal", "Macro", "Manager", "Operator",
"Report", "Report Template", "Rule", "State-Based Rule", "Table",
"Table Template", and "Time-Based Rule" are used without modification
from the definitions provided in [I-D.ietf-dtn-dtnma].
Additional terms defined in this document are as follows.
Application: A software implementation running on an Agent and being
managed by a Manager. This includes software that implements
protocol processing on an Agent.
Application Management Model (AMM): The object and literal-value
model defined by this document in Section 3 and implemented as
instances in ADMs and ODMs.
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Application Resource Identifier (ARI): A unique identifier for any
AMM object, namespace, or literal value. The text form of an ARI
is conformant to the Uniform Resource Identifier (URI) syntax
documented in [RFC3986] and using the scheme name "ari".
Application Data Model (ADM): The set of statically-defined objects
necessary to manage an application asynchronously. This is also
the name for the specific syntax used to express the contents of
that ADM, as defined in another document.
Operational Data Model (ODM): The set of dynamically-defined objects
created and controlled by Managers in the network. There is
currently no specific syntax used to express the entire contents
of an ODM outside of data from introspection reports generated by
an Agent.
Namespace: Each ADM and ODM has a universally unique identifier and
acts as a namespace for a set of AMM objects.
2. Data Modeling Concept of Operations
In order to asynchronously manage an application in accordance with
the [I-D.ietf-dtn-dtnma], an application-specific data model must be
created containing static structure for that application. This model
is termed the Application Data Model (ADM) and forms the core set of
information for that application in whichever network it is deployed.
ADM structure and base ADMs are discussed in detail in Section 4.
The objects codified in the ADM represents static configurations and
definitions that apply to any deployment of the application,
regardless of the network in which it is operating. Within any given
network, Managers supplement the information provided by ADMs with
dynamic objects. Each namespace of dynamic objects is termed an
Operational Data Model (ODM) and is discussed in detail in Section 5.
Both the ADMs and ODMs rely on a common meta-model, the Application
Management Model of Section 3, which defines the basic structure of
what kinds of types and objects are available to use within the
DTNMA. The relationships among the AMM, ADM, and ODM are illustrated
in Figure 1. Together, the set of objects in the union of all
supported ADMs with dynamic ODM objects forms the data model used to
manage an Agent.
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+---------------+
| AMM |
| (object types)|
+-------^-------+
|
+-------+-------+
| |
+-----+-----+ +-----+-----+
| ADM | | ODM |
|(instances)| |(instances)|
+-----------+ +-----------+
Figure 1: Data Model Relationships
The AMM defines a strict separation between long-lived object
instances and ephemeral value instances. While an Agent hosts the
object instances, each manager must contain the corresponding ADM and
ODM definitions in order to identify and interact with those objects.
Those interactions are performed using Application Resource
Identifiers (ARIs) as depicted in Figure 2.
+-------------+ +-------------+
| AMM Value | | AMM Object |
| (in ARI) | | (in model) |
+------^------+ +-------------+
| ^
| subtypes |
+-------+-------+ |
| | | referenced
+-----+-----+ +-----+-----+ | object
| Literal | | Object |-----------+
| | | Reference |
+-----------+ +-----------+
Figure 2: AMM Value and Object Relationships
While an agent hosts the actual object instances, each manager must
contain the corresponding ADM and ODM definitions in order to
identify and interact with those objects. Those interactions are
performed using Application Resource Identifiers (ARIs) as depicted
in Figure 3.
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+------------------------------------------+
| |
| +-------+ +-------+ +-------+ |
| | ADM 1 | | ADM 2 | | ODM 1 | |
| | def'n | | def'n | | def'n | |'
| +-------+ +-------+ +-------+ |
| ... ... |
| +-------+ +-------+ |
| | ADM N | | ODM M | |
| | def'n | | def'n | |
| +-------+ +-------+ |
| Manager instance |
+------------------------------------------+
^^
||
ARI values
||
vv
+------------------------------------------+
| |
| +-------+ +-------+ +-------+ |
| | ADM 1 | | ADM 2 | | ODM 1 | |
| | objs | | objs | | objs | |
| +-------+ +-------+ +-------+ |
| ... ... |
| +-------+ +-------+ |
| | ADM N | | ODM M | |
| | objs | | objs | |
| +-------+ +-------+ |
| Agent instance |
+------------------------------------------+
Figure 3: Agent and Manager Interaction
2.1. Values and Value-Producing Objects
The ARI of [I-D.ietf-dtn-ari] is used as the basis for the values
used internally for Agent Processing activities and for the basis of
Agent-Manager Messaging contents.
Of the value-producing object types discussed in Section 3.4 and
Section 6.5, the functions of these objects are summarized and
compared with literals in Table 1 and the following list. In that
table, "internal" means values are managed by the Agent itself and
"external" means the source of values is outside the Agent.
Literal Values: ARI literals are, by definition, immutable and fully
self-contained values.
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For example, the number 4 is a literal value. The name "4" and
the value 4 represent the same thing and are inseparable. Literal
values cannot change ("4" could not be used to mean 5) and they
are defined external to the autonomy model (the autonomy model is
not expected to redefine what 4 means).
Constant (CONST): These objects are named values which are defined
in specific revisions of an ADM and produced directly by the Agent
implementing the ADM. Both the name and the value of the constant
are fixed and cannot be changed (within a revision).
An example of a constant would be defining the numerical value
_pi_ to some predetermined precision.
Variable (VAR): These objects are named value storage entities which
are defined in ADMs or ODMs and managed by the Agent implementing
the ADM or ODM. While the name is constant the value can change
over time due to controls acting upon the Agent. One standard
interface is an ADM-defined initial state expression with a
control available to reset to that initial state (which can itself
reference other value producing objects and operators). Another
standard interface is a control to set a variable to a specific
value.
An example of a variable using just its initial expression would
be an accumulator summing together a list of counter values
produced by other objects. An example of a manager-controlled
variable would be a threshold value used to compare against a
sensor value in a rule predicate.
Externally Defined Data (EDD): These objects are named entities
which are defined in an ADM but produce values based on data
provided to an Agent from its environment. These values are the
foundation of state-based autonomy as they capture the state of
the managed device. The autonomy model treats these values as
read-only state. It is an implementation matter to determine how
external data is transformed into values of the specific type
specified for an EDD.
Examples of externally defined values include temperature sensor
readings and the instantaneous data rate from a modem or radio.
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+==========+===========+=========+
| | Immutable | Mutable |
+==========+===========+=========+
| Internal | CONST | VAR |
+==========+-----------+---------+
| External | _Literal_ | EDD |
+==========+-----------+---------+
Table 1: Value-Producing
Object Types
2.2. Agent Processing
Based on the reasoning described in [I-D.ietf-dtn-dtnma], much of the
closed-loop processing of the state of the DTNMA Agent is performed
on the Agent itself using rule objects. The different types of
processing performed on the Agent are separated into Execution,
Evaluation, and Reporting with corresponding AMM object types related
to each of these as indicated in Table 2 (_e.g._, execution relates
to CTRL objects but not OPER objects). Some of the objects defined
in the Agent ADM (Section 4.3) combine the use of these processing
activities, but they are still independent of each other. There is
no mixing of activities such as executing a control within an
expression; although the execution of a control can result in an
expression being evaluated they are independent activities.
Within the runtime of an Agent any input, output, and intermediate
values can use the concept of a semantic type (Section 3.3) to do
things like restrict the valid numeric range of a value or allow a
union of disjoint types to be present (_e.g._, a certain value can be
a boolean or an unsigned integer). This is combined with the built-
in types available (see Section 3.2) to allow complex type
information to be present in an ADM or ODM without requiring
additional over-the-wire encoding size. A Type Conversion activity
is defined for when implicit or explicit type conversion is needed.
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+==================+=================+========+
| Activity | Objects | Values |
+==================+=================+========+
| Execution | CTRL | MAC |
+------------------+-----------------+--------+
| Evaluation | OPER, TYPEDEF | EXPR |
+------------------+-----------------+--------+
| Reporting | _N/A_ | RPTT |
+------------------+-----------------+--------+
| Value Production | CONST, EDD, VAR | _N/A_ |
+------------------+-----------------+--------+
| Type Casting | TYPEDEF | _N/A_ |
+------------------+-----------------+--------+
| Rule Autonomy | SBR, TBR | _N/A_ |
+------------------+-----------------+--------+
Table 2: Processing Activities and Object Types
2.3. Agent-Manager Messaging
This document does not define a messaging protocol between agents and
managers but full functioning of this data model behavior does rely
on the following types of messages being available. Because each
message is based on ARI value types, they can be implemented in Agent
and Manager by encoding the associated ARI according to a network-
specific transport profile. The choice of encoding form, framing, or
transport are implementation matters outside of this specific
document.
Execution: This message causes an Execution of a referenced
parameterized CTRL object (Section 3.4.5) or MAC value
(Section 4.2.4). The form of this message is an Execution-Set
(EXECSET) value. This type of message is only sent from Manager
to Agent. Each message can contain multiple execution targets but
all must be associated with the same nonce value. It is an
implementation detail whether a Manager sends fewer messages with
more targets or more timely messages with fewer targets.
Reporting: This message carries the reports generated by Reporting
activities and as the result of Execution when the Manager
provides a correlator nonce. The form of this message is an
Reporting-Set (RPTSET) value. This type of message is only sent
from Agent to Manager. Each message can contain multiple report
containers but all must be associated with the same nonce value.
It is an implementation detail whether an Agent sends fewer
messages with more reports or more timely messages with fewer
reports.
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The contents of these messages, individual fields, are representable
by ARI values so require only small additional message-type
identifying and framing overhead to bind to whatever transport is
being used (_e.g._ the Bundle Protocol).
3. Application Management Model (AMM)
This section describes the Application Management Model, which is the
meta-model used to implement the DTNMA. This section also provides
additional information necessary to work with this model, such as:
literal value types, object structure, naming conventions, and
processing semantics.
The overall AMM is decomposed into two categories:
Objects: These are the structural and behavioral elements of the
AMM, present in ADMs and ODMs. Objects implement the actual
purpose of the applications being managed; they extract values
from the Agent's environment, operate on expressions, store
variables, and execute controls to affect the Agent's environment.
Because objects are behavioral they have no complete static
representation, objects are only ever described and identified.
AMM object types are defined in Section 3.4 and objects are
instantiated as part of an ADM or ODM.
Values: These are the runtime state and intermediates of the AMM,
present in the Agent's state but not directly in ADMs or ODMs.
Objects produce, operate on, and store or consume values and these
values are what are present in messaging between Managers and
Agents. AMM values are explained in more detail in Section 3.1.
One subset of AMM values are object references used to identify
(and parameterize) individual AMM objects.
3.1. AMM Values
Values within the AMM have two top-level classes: literal values, and
object reference values. Each of these is discussed more detail in
the following subsections. Both classes of AMM values are related to
what can be represented externally as an ARI, as described in
Section 3.1.3.
3.1.1. Literal Values
Literal values are those whose value and identifier are equivalent.
These are the most simple values in the AMM. For example, the
literal "4" serves as both an identifier and a value.
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Because the Literal value serves as its own identifier, there is no
concept of a parent namespace or parameters. A literal can be
completely identified by its data type and data value.
Literals have two layers of typing:
Built-In Type: This is the lower layer which defines the syntax of
the literal value and bounds the domain of the value (_e.g._ a
BOOL has two possible values, while an INT has a large domain of
integers). There are a small number of built-in types as
described in Section 3.2 and they are managed with an IANA
registry defined in Section 9.3 of [I-D.ietf-dtn-ari].
Semantic Type: This is the higher layer which defines additional
semantics to a value, such as a restricted domain of values or a
human-friendly text unit or limits on the items of an ARI
collection. Semantic types are defined within ADMs (see
Section 3.3 and Section 3.4.2), so there can be an arbitrary
number of them and they are managed outside of a central
authority.
All literal values have a concrete and stand-alone representation
independent of any ADM or ODM behavior in the form of an ARI
(Section 3.1.3) and a value itself has no direct association with a
semantic type outside of a specific context in which that type is
used (_e.g._, Section 6.10 and Section 6.11).
3.1.2. Object Reference Values
Every object in the AMM is uniquely identifiable, regardless of
whether the item is defined statically in an ADM or dynamically in an
ODM. Object reference values are composed of four parts: a
namespace, an object type, an object name, and object-specific
optional parameters.
AMM objects are identified within unique namespaces to prevent
conflicting names within network deployments, particularly in cases
where network operators are allowed to define their own object names.
In this capacity, namespaces exists to eliminate the chance of a
conflicting object name. They MUST NOT be used as a security
mechanism. An Agent or Manager MUST NOT infer security information
or access control based solely on namespace information.
Two categories of namespaces available within the object reference
value and the ARI syntax:
ADM Namespace: These are defined, with text-name and enumeration, in
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an IANA registry of ADMs in Section 9.3 of [I-D.ietf-dtn-ari].
There is also a reservation of private-use code points for domain-
and mission-specific ADMs. In ARI form, ADM namespaces are
present as either their name or enumeration directly.
ODM Namespace: These are defined, with text-name and enumeration, in
an IANA registry of ODMs in Section 9.3 of [I-D.ietf-dtn-ari]. It
is expected that most ODM use will be domain- and mission-
specific. In ARI form, ODM namespaces are present as a "!"
prefixed name or as a negative-value enumeration.
Object types, each with a text-name and enumeration, are defined in
an IANA registry by Section 9.3 of [I-D.ietf-dtn-ari].
Object names are text strings and enumerations whose value is
determined by the creator of the object. For those objects defined
in an ADM, the structure of the object name is given in
Section 3.4.1.
3.1.2.1. Parameters
Parameterization is used in the AMM to enable expressive autonomous
function and reduce the amount of traffic communicated between
Managers and Agents. In the AMM, most objects can be parameterized
and the meaning of parameterization for each object type is defined
in Section 3.4 with behaviors related to parameters defined in
Section 6.
There are three notions of parameters defined in the AMM, which take
their name from computer programming vernacular used for discussing
function declarations and function calls, those are: formal
parameters, given parameters, and actual parameters. Formal
parameters are discussed in Section 3.4.1 while given and actual
parameters are discussed here in relation to the object reference.
Given parameters represent the data values passed to a parameterized
AMM Object at runtime. They "fulfill" the parameter requirements
defined by the formal parameters for that object. Each object type
can have a slightly different notion of how its parameters affect its
processing activities.
A given parameter MUST include a value and MAY include a type. If a
type is provided it MUST be consistent with the type provided by the
corresponding formal parameter.
There are two ways in which the value of an given parameter can be
used:
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Parameter by Value: This method involves directly supplying the
value as part of the given parameter. It is the most direct
method for supplying values.
Parameter by Label: This method involves supplying the LABEL of some
other processing-context-specific value and substituting, at
runtime, that named value as the value of this parameter. This
method is useful when a parameterized AMM Object produces a value
that references a parameter of the producing object. The produced
value's given parameter can be given as the LABEL of the producing
object's formal parameter. In this way, a value-producing
object's parameters can "flow down" to all of the values that it
produces.
In cases where a formal parameter contains a default value, the
associated given parameter may be omitted. Default values in formal
parameters (and, thus, optional given parameters) are encouraged as
they reduce the size of data items communicated between Managers and
Agents in a network.
Finally, actual parameters are the result of applying the Parameter
Handling procedure to normalize a set of given parameters based on a
set of formal parameters from a processing context.
3.1.3. The Application Resource Identifier (ARI)
The Application Resource Identifier (ARI) is used to represent AMM
values outside of an Agent or Manager (_i.e._ in messaging between
them) and is defined in [I-D.ietf-dtn-ari]. Another function of the
ARI is for diagnostic or configuration purposes within either
Managers or Agents. It is important to make the distinction that
within an AMM entity (Agent or Manager) the semantic type of a value
is kept, but when exchanged via ARI the semantic type is lost. The
AMM defines type compression and reconstruction rules in Section 6.12
to handle this.
3.2. Built-In Types
This section describes the built-in types used for AMM values, which
are those usable directly with ARI syntax. By definition, literal
values are self-contained and literal types restrict the form and
function of those values.
All built-in types within the AMM exit within a flat namespace, but
some types have complex relationships with other types beyond the "is
a" concept of type inheritance. Built-in types are defined within
the "Literal Types" and "Managed Object Types" sub-registries of
[IANA-DTNMA] and explained in this section. The following
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subsections divide the types into groups to simplify their
explanation, not because of an intrinsic relationship within each
group.
These lists of built-in type names are not fixed in any single
specification, and require standards action to add to and update URI
processors to handle them, so it is expected that this list will be
relatively static (compared to the expected rate of addition or
changes to ADMs).
3.2.1. Simple Types
Simple types are those which cannot be subdivided and represent an
"atomic" value within the AMM type system. They correspond roughly
with the CBOR primitive types Section 3.3 of [RFC8610]. The simple
types are summarized in Table 3.
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+=========+==================================================+
| Type | Description |
+=========+==================================================+
| NULL | The singleton null value. |
+---------+--------------------------------------------------+
| BOOL | A native boolean true or false value. |
+---------+--------------------------------------------------+
| BYTE | An 8-bit unsigned integer. |
+---------+--------------------------------------------------+
| INT | A 32-bit signed integer. |
+---------+--------------------------------------------------+
| UINT | A 32-bit unsigned integer. |
+---------+--------------------------------------------------+
| VAST | A 64-bit signed integer. |
+---------+--------------------------------------------------+
| UVAST | A 64-bit unsigned integer. |
+---------+--------------------------------------------------+
| REAL32 | A 32-bit [IEEE.754-2019] floating point number. |
+---------+--------------------------------------------------+
| REAL64 | A 64-bit [IEEE.754-2019] floating point number. |
+---------+--------------------------------------------------+
| TEXTSTR | A text string composed of (unicode) characters. |
+---------+--------------------------------------------------+
| BYTESTR | A byte string composed of 8-bit values. |
+---------+--------------------------------------------------+
| TP | An absolute time point (TP). |
+---------+--------------------------------------------------+
| TD | A relative time difference (TD) with a sign. |
+---------+--------------------------------------------------+
| LABEL | A text label of a parent object parameter. This |
| | is only valid in a nested parameterized ARI. |
+---------+--------------------------------------------------+
| CBOR | A byte string containing an encoded CBOR item. |
| | The structure is opaque to the Agent but |
| | guaranteed well-formed for the ADM using it. |
+---------+--------------------------------------------------+
| ARITYPE | An integer value representing one of the code |
| | points in this Literal Types table. |
+---------+--------------------------------------------------+
Table 3: Simple Literal Types
The following subsections discuss nuances in sub-groups of these
simple types.
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3.2.1.1. Discrete Value Types
The NULL and BOOL types are used to limit to specific discrete
values. Because there are CBOR primitive types corresponding exactly
with these AMM types, generators of ARIs with these types can always
be compressed by eliding the literal type as defined in Section 6.12.
The NULL type has only a single value, null, which is not useful for
expressions or type casting but is useful for defining union types
which have "optional value" semantics where the null value is used to
indicate the absence of a normal value.
The BOOL type is useful for type casting (Section 6.11.1) where an
arbitrary value is treated as "truthy" or "falsey" in a context such
as a State-Based Rule (SBR) condition.
3.2.1.2. Numeric Types
All of the numeric types (BYTE, UINT, INT, UVAST, VAST, REAL32, and
REAL64) exist within a domain where values can be converted between
types (Section 6.11.2). Some cases of implicit casting is done for
type promotion as necessary for arithmetic operations.
3.2.1.3. Absolute (TP) and Relative (TD) Time Types
The TP type represents an instant in time in the UTC datum. When in
text form it is formatted in accordance with the date-time symbol of
Appendix A of [RFC3339] and always in the "Z" time-offset.
The TD type represents an offset in time from a relative epoch
instant, either later than (a positive offset) or earlier than (a
negative offset). When in text form it is formatted in accordance
with the duration symbol of Appendix A of [RFC3339] with a positive
or negative sign prefix. The epoch instant of a relative time MUST
be unambiguously defined in the context using the time value.
| In cases where a type signature contains an union of TP and TD
| (i.e. an option for either type), relative times have some
| advantages over absolute times: they do not require time to be
| synchronized across Agents and Managers, and they are more
| compact in their representation. For example, expressing the
| semantics "run control_one 10 seconds after receiving it" or
| "run control_two 20 seconds after running control_one" is more
| appropriate using relative times than absolute times.
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3.2.2. Containers
AMM objects, or parameters associated with those objects, often need
to represent groups of related data or more complex nesting of data.
These are the literal types for AMM value containers, which can only
be present in a typed-literal ARI form.
The AMM defines three collection literal types (AC, AM, and TBL) and
allows ADMs to combine these literal types with a complex pattern
syntax to create semantic types constraining their contents (_e.g._,
for macros and expressions in Section 4.2.3).
3.2.2.1. ARI Collection (AC)
An ARI Collection (AC) is an ordered list of ARI elements. The
contents of an AC can be restricted in size and type by the use of a
semantic type (Section 3.3).
An AC is used when there is a need to refer to multiple AMM values as
a single unit. For example, when defining a Report Template, the
definition has an AC that defines the ordered ARIs whose values
constitute that report.
3.2.2.2. ARI Map (AM)
An ARI Map (AM) is a mapping from a set of "key" ARIs to arbitrary-
typed "value" ARIs. As defined in [I-D.ietf-dtn-ari] the AM keys are
limited to untyped literals, while the AM values can be any type.
The contents of an AM can be restricted in size and type by the use
of a semantic type (Section 3.3).
An AM is used when there is a need to define data structures with
complex, optionally present attributes. For example, as control
parameters used to define new objects in an ODM.
3.2.2.3. ARI Table (TBL)
An ARI Table (TBL) is a collection of values which are logically
structured as a two dimensional table of rows and columns, with each
cell of the table containing an AMM value.
Although the contents of a TBL can be handled independently of any
data model, the meaning of a TBL can only be interpreted within the
context of a Table Template (TBLT) defined within an ADM. The TBLT
takes the form of a structured type definition on a value-producing
object which defines the columns of the table, including each of
their column names and types and optional constraints on the number
of and uniqueness of rows in the TBL.
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A TBL is used when an EDD represents a set or list of complex items
as rows in a table. For example, the Agent ADM reports its own set
of supported ADMs and features as a TBL (see the "capability"
object).
3.2.2.4. Execution-Set (EXECSET)
An Execution-Set (EXECSET) is a collection of values used as targets
for the Execution activity. Each message can reference multiple
execution sources (CTRL and MAC) and, unlike the MAC execution
itself, can be handled by executing multiple items in parallel.
The contents of an EXECSET value are as follows:
Correlator nonce:
This field is an optional opaque correlator "nonce" which can be
used to indicate that the result of the corresponding CTRL
execution is desired to be reported back to the Manager. The
value is limited to match the NONCE (Section 4.2.2) type.
Targets:
This is an unordered list of targets to be executed by an Agent.
Each execution target is limited to match the exec-tgt
(Section 4.2.6) type.
3.2.2.5. Reporting-Set (RPTSET)
A Reporting-Set (RPTSET) is a collection of report containers, where
each report container consists of a timestamp and an ordered list of
data values populated in conformance to a source object being
reported on. Reporting-Set values and reports themselves do not have
individual identifiers, rather they are identified by their source
and the timestamp at which their data values were collected.
The contents of an RPTSET value are as follows:
Correlator nonce:
This field is an optional opaque correlator "nonce" which is used
to associate report containers with specific EXECSET messages
which caused the reports to be generated. The value is limited to
match the NONCE type (Section 4.2.2).
Reference time:
This field is used as an absolute reference time for all reports
contained in the RPTSET. The value is limited to match the TP
built-in type. It is used as an storage optimization when a large
number of reports are generated around the same time.
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Report list:
The main content of the RPTSET are the reports themselves, which
are defined below. The order of reports within the RPTSET are not
significant, and the presence of a report in any particular RPTSET
is not significant. The RPTSET itself is only a container.
The contents of each report within a RPTSET are as follows:
Source:
The source of the report in the form of an ARI with an object-
reference for one of the following types: VALUE-OBJ
(Section 4.2.2), or CTRL. If the source was parameterized, this
ARI SHALL contain the actual parameters used at the time of
reporting.
Generation Time:
The timestamp at which the report items were sampled, relative to
the Reference Time of the containing RPTSET. The value is limited
to match the TD built-in type.
Correlator nonce:
This value is identical to the nonce from the EXECSET which caused
the associated reports to be generated, or the null value if the
report is not associated with an execution activity. The value is
limited to match the NONCE type (Section 4.2.2).
Items:
A list of values corresponding to the source object, with
cardinality according to the following:
* For a VALUE-OBJ source the item list SHALL be the result of
reporting (Section 6.8.2) on that object.
* For a CTRL-REF source there SHALL be a single value
representing the Result of the execution. A result of
undefined indicates a failure executing the CTRL.
3.2.3. Object Reference Types
For each of the AMM Object Types there is a corresponding object
reference type. The object type names and enumerations from the
"Managed Object Types" sub-registry of [IANA-DTNMA] are used as names
for the built-in type of the corresponding object reference.
For example, a reference value for a CTRL object is typed as CTRL.
It is important to understand the distinction, illustrated in
Figure 2, between the built-in type and the object type both of which
have the same name but used in two completely independent contexts.
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3.2.4. Value-Class Types
As a special case of built-in type which act as a union or class of
types are those listed in Table 4. These are implemented as a built-
in type rather than a semantic type because they behave differently
than a Type Union (Section 3.3.6) because they will match any value
in the associated class and conversions within these types will not
affect the value.
+=========+======================================+
| Type | Description |
+=========+======================================+
| LITERAL | Any possible literal value. |
+---------+--------------------------------------+
| OBJECT | Any possible object reference value. |
+---------+--------------------------------------+
Table 4: Value-Class Types
3.2.5. Custom Types
When an application requires a more complex or specialized literal
type than one already available the preferred design procedure is as
follows:
1. If an existing ADM already defines a semantic typedef (see
Section 3.4.2) it is RECOMMENDED to import that ADM and use its
typedef.
2. Otherwise, when it is possible to use an ADM-defined semantic
typedef to achieve the desired goals it is RECOMMENDED to do so.
3. Otherwise, when the desired behavior cannot be accomplished by a
semantic typedef, it is RECOMMENDED to use the opaque CBOR type
with interface documentation to explain the syntax of the encoded
CBOR item.
4. Otherwise, the application MAY make use of the private-use block
of literal type code points.
Implementing a custom literal type requires implementation effort on
both an Agent and its associated Manager(s) as well as being more
opaque to diagnostic tools and middleboxes.
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3.3. Semantic Types
While built-in types control the basic syntax and domain of AMM
values, the concept of semantic type is to provide a means to augment
literal types by expanding (via union), narrowing (via constraints),
and adding human-friendly annotation (such as references to defining
documents, or explanations of purpose).
Semantic types can be defined in two ways: a named Semantic Type
Definition (TYPEDEF) or an anonymous semantic type defined at the
point of use (_e.g._, within an AMM object definition). The specific
syntax used to define semantic types within an ADM are defined and
explained in a separate document.
When a "type" is needed for an AMM value in an object definition it
SHALL be either one of the built-in types, a namespace-qualified
semantic type, or an anonymous semantic type just for that value.
The actual mechanics of semantic typing are based on the classes
defined in the following subsections.
3.3.1. Named Type Use
The simplest case is where an existing named type is referenced to be
used in a specific context. The form of a named type use SHALL be an
AMM value containing either an ARITYPE literal, for a built-in type
(Section 3.2), or a TYPEDEF object reference, for a data-model-
provided semantic type (Section 3.4.2).
Even an unconstrained type reference can be used within a TYPEDEF to
provide a human-friendly name or associated documentation for the use
of a simple type. While the tooling might not care about direct type
use, it can greatly improve human interpretation of a data model.
An implementation SHALL be able to handle situations where type
references create a loop. This would allow values to follow a
recursive structure, but it does not mean the values themselves would
be of an indefinite size.
Within a named type use, annotations can be added which enhance human
understanding of the type. Annotations possible within a named type
use SHALL consist of:
* A free-form text reference to a specific document defining the
type in more detail.
* A free-form text description of the type, which can be in addition
to a reference.
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* A units name for NUMERIC values to make the interpretation of
values more explicit.
* A display hint to enable type-specific handling of values, such as
IP addresses within BYTESTR values.
Within a named type use, constraints can be added to some of the
Simple Types in order to limit what values are considered valid
within the type domain. Constraints possible within a named type use
SHALL consist of:
* Limits on ranges of valid NUMERIC types
* Limits on length of TEXTSTR, BYTESTR, or CBOR
* Labels of enumerated values or bit positions for INTEGER types
* Regular expression patterns for TEXTSTR
* Structural patterns for CBOR items using Concise Data Definition
Language (CDDL)
3.3.2. Uniform List
This is the case of a list of AMM values within an ARI Collection
(AC) where the type of each value is uniform for the whole list.
Only the AC type MAY be refined by a uniform list. Each item of a
uniform list SHALL be constrained to a single semantic or built-in
type. The number of items in the list MAY be constrained within a
range of valid sizes.
3.3.3. Diverse List
This is the case of a list of AMM values within an ARI Collection
(AC) where the type of each value is different throughout the list.
Only the AC type MAY be refined by a diverse list. Each part of a
uniform list SHALL be constrained as either: an item with a single
semantic or built-in type or a Sequence (Section 3.3.7).
3.3.4. Uniform Map
This is the case of a map of AMM values within an ARI Map (AM) where
the type of each key and each value is uniform for the whole map.
Only the AM type MAY be refined by a uniform map use.
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3.3.5. Table Template
This is the case of a table of AMM values within a ARI Table (TBL)
where each column is annotated with a text name and the type of each
value in a column is uniform across all rows. Only the TBL type MAY
be refined by a table template. The number of rows in the table MAY
be constrained within a range of valid sizes. A single "key" column
SHOULD be identified as the unique identifier for each row. One or
more column tuples MAY be identified as unique among all rows.
3.3.6. Type Union
This creates a choice between a combination of multiple semantic
types. Each of the types in a union SHOULD be exclusive to avoid
ambiguity in interpretation by a value processor. The order of
choices within a union SHALL be used as the order to check for Type
Matching and Type Conversion procedures.
3.3.7. Sequence
This creates a subset of a Diverse List (Section 3.3.3) which matches
multiple sequential elements of the list. A sequence is similar to a
Uniform List except that it doesn't specify an AC container, it is
used to specify items _within_ a container. Each item of a sequence
SHALL be constrained to a single semantic or built-in type. The
number of items in the sequence MAY be constrained within a range of
valid sizes.
A sequence can also be used with formal parameters to create a form
of variadic parameter, where multiple given parameters are matched
and combined into a single actual parameter (see Section 6.4).
3.4. AMM Object Types
This section identifies the types of objects that make up the AMM and
which are instantiated within each ADM and ODM. Each object type is
defined by its logical structure and its behavior in Value
Production, Execution, or Evaluation contexts within Agents. Each
type can allow or disallow parameters within objects and, due to
processing behaviors, can either allow or disallow use within an ADM
or ODM.
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The names for the types of objects defined in this section can be
used in two different and separate contexts: as a name for the type
of the object itself (written as plain text within this document)
when in the context of the AMM object model, or as the name of an
object reference (Section 3.1.2) type (written in typewriter text
within this document) when used in the context of the AMM value
model.
Unless explicitly specified in the object type subsection, an object
SHALL NOT be parameterized.
3.4.1. Common Object Fields
Every object type in the AMM includes a set of fields providing
annotative or otherwise user-friendly descriptive information for the
object. This information may be used as documentation (for example,
only present in ADMs and on operator consoles) and/or encoded and
transmitted over the wire as part of a management protocol.
The metadata supported by the AMM for all objects is as follows:
Name:
An object name is a text string associated with the object, but
does not constitute the sole identifier for the object. Names
provide human-readable and/or user-friendly ways to refer to
objects with the text form of an ARI. Each object definition
SHALL contain a name field. An object's name SHALL NOT change
between ADM revisions. Each name SHALL conform to the id-text
ABNF symbol of Section 4 of [I-D.ietf-dtn-ari]. Within each
namespace and object type, the name of an object SHALL be unique.
Enumeration:
An object enumeration is an integer associated with the object,
which identifies the object just like its name. Object
enumerations provide a stable and concise identifier for the
binary encoded form of an ARI. Each object definition SHOULD
contain an enumeration field. An object's enumeration SHALL NOT
change between ADM revisions. When present, each enumeration
SHALL be an unsigned integer value. Within each namespace and
object type, the enumeration of an object SHALL be unique.
Status:
Each object definition MAY contain a status field. The valid
status values of an object are the same as the valid status values
for an ADM in Section 4.1.1. In the absence of a status field,
the status of the object SHALL be considered the same as the
status of the ADM which contains it.
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Reference:
Each object definition MAY contain a reference field. A reference
is a text string referring to a specification or other document
which details the source or purpose of the object.
Description:
Each object definition MAY contain a description field. A
description is a text string explaining the purpose or usage of
the object in a human-readable format. There is no minimum or
maximum size of description text for an object. The description
serves as documentation for the object and SHOULD be the same
regardless of how the object might be parameterized. For example,
the description of a CTRL object should document the purpose of
the CTRL in a way that is independent of the value of any
particular parameter value passed to that CTRL.
Formal parameters define a method to customize an AMM object. When
used by an object definition, it's formal Parameters SHALL be an
ordered list of individual formal parameter definitions. Each formal
parameter SHALL include type and name. Each formal parameter MAY
include an optional default value. The application of default
parameters and relationship of actual parameters (Section 3.1.2.1) to
formal parameters is defined in Section 6.4.
3.4.2. Semantic Type Definition (TYPEDEF)
An ADM can define a semantic type definition (TYPEDEF) to give a name
to a semantic type (Section 3.3). This TYPEDEF name can then be used
as a type anywhere else in the same ADM or another one which imports
it.
The definition of a TYPEDEF consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Type:
A TYPEDEF definition SHALL include the type being named, as
described in Section 3.3. The type of a TYPEDEF is fixed and
SHALL NOT change between ADM revisions. The type SHALL be either
a union of other types or a restriction of or annotation upon
another type.
As defined in this document, TYPEDEFs and semantic types can only be
defined within an ADM. Future capability could allow the use of
TYPEDEFs within ODMs.
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3.4.3. Externally Defined Data (EDD)
Externally defined data (EDD) objects represent data values that are
produced based on a source external to the Agent itself. The Value
Production occurs at the moment the value is needed, by either an
Evaluation or a Reporting activity. The actual value could come from
outside of the Agent proper, or be derived from data outside of the
Agent.
The value production of an EDD SHOULD be nilpotent and have no side-
effects in the processor. This property is not enforced by the Agent
but requires consideration of the ADM designers, see Section 7.
The value produced by an EDD is allowed to, but not required to,
change over time. Because EDDs can be referenced by condition
expressions of Time-Based Rules (Section 3.4.8) or elsewhere, an
Agent implementation could be optimized by allowing an EDD to
indicate when its produced value _would_ change. It is an
implementation matter for if and how an application can provide that
indication.
For values managed entirely within the Agent use a Variable (VAR) or
for constant-values use a Constant (CONST). For complex tabular
data, use an EDD with a type which produces an ARI Table (TBL).
The definition of an EDD consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Parameters:
An EDD definition MAY include ARI parameters to be used when the
EDD is used to produce a value. Parameterized objects are
discussed in Section 7. The parameters of an EDD are fixed and
SHALL NOT change between ADM revisions.
Type:
An EDD definition SHALL include the type of the value produced by
the object, as described in Section 3.3. The type of an EDD is
fixed and SHALL NOT change between ADM revisions.
As defined in this document, EDDs can only be defined within an ADM.
Future capability could allow the use of EDDs within ODMs.
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3.4.4. Constant (CONST)
A Constant (CONST) represents a named literal value, but unlike an
Externally Defined Data (EDD) or Variable (VAR) a CONST always
produces the same value. Examples include common mathematical values
such as PI or well-known time epochs such as the UNIX Epoch. A CONST
typed to produce a simple value can be used within an expression (see
Section 6.7), where the object is used to produce a value at the
moment of evaluation. A CONST can also be typed to produce an EXPR
value to evaluate, or MAC value to execute.
The definition of a CONST consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Type:
A CONST definition SHALL include the type of the value produced by
the object, as described in Section 3.3. The type of a CONST is
fixed and SHALL NOT change between ADM revisions.
Value:
A CONST definition SHALL include the literal value produced during
evaluation.
As defined in this document, CONSTs can only be defined within an
ADM. Allowing network operators to define constants dynamically
means that a Constant could be defined, removed, and then re-defined
at a later time with a different value, which defeats the purpose of
having Constants. When adding new "fixed" values to an ODM, a
Variable (VAR) MUST be used instead of a Constant.
3.4.5. Control (CTRL)
A Control (CTRL) represents a predefined function that can be
executed on an Agent. Controls are not able to be defined as part of
dynamic network configuration since their execution is typically part
of the firmware or other implementation outside of the Agent proper.
The execution of a CTRL SHOULD be idempotent and have no effect if
executed multiple times in sequence. This property is not enforced
by the Agent but requires consideration of the ADM designers, see
Section 7.
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Controls can be executed in a "one shot" manner as part of messaging
from a Manager to an Agent. Network operators that wish to
autonomously execute functions on an Agent may use a State-Based Rule
(SBR) or Time-Based Rule (TBR). When an execution involves the
ordered sequence of controls, a Macro (MAC) SHOULD be used instead of
a more fragile use of CTRL directly.
The definition of a CTRL consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Parameters:
A CTRL definition MAY include ARI parameters to be used when the
CTRL is executed. Parameterized objects are discussed in
Section 7.
Result:
A CTRL definition MAY include the definition of a result. The
result SHALL have a name and a type. The result MAY have a
default value. The result of a CTRL is separate from the
execution status as being successful or failed.
As defined in this document, CTRLs can only be defined within an ADM.
Future capability could allow the use of CTRLs within ODMs if there
was some mechanism to bind a CTRL definition to some platform-
specific execution specification (_e.g._, a command line sequence).
3.4.6. Operator (OPER)
An Operator (OPER) represents a user-defined, typically mathematical,
function that operates within the evaluation of an Expression (EXPR).
It is expected that operators are implemented in the firmware of an
Agent.
The AMM separates the concepts of Operators and Controls to prevent
side-effects in Expression evaluation (e.g. to avoid constructs such
as A = B + GenerateReport()). For this reason, Operators are given
their own object type and Controls do not interact with operators.
The definition of an OPER consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
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Parameters:
An OPER definition MAY include ARI parameters to be used when the
OPER is evaluated. Parameterized objects are discussed in
Section 7. The parameters of an OPER are distinct from the
operands from the expression stack.
Operands:
An OPER definition MAY include definitions of operand values to be
popped from the expression stack when the OPER is evaluated. Each
operand SHALL consist of a name, a type, and a cardinality. Any
non-trivial OPER will have one or more operands. An OPER can have
a non-fixed operand count which is based on a parameter value
(_e.g._, an operator can average the top _N_ values from the
stack, where _N_ is a parameter).
Result:
An OPER definition SHALL include definition of a result value to
be pushed onto the expression stack after the OPER is evaluated.
The result SHALL have a name and a type. The result SHALL NOT
have a default value.
As defined in this document, OPERs can only be defined within an ADM.
Future capability could allow the use of OPERs within ODMs if there
was some mechanism to bind an OPER definition to some platform-
specific evaluation specification.
3.4.7. State-Based Rule (SBR)
A State-Based Rule (SBR) is a form of autonomy in which the Agent
performs an action upon the change of state to meet a specific
condition. The execution model of the SBR is to evaluate the
Condition (as often as necessary to handle changes in its expression
evaluation) and when it evaluates to a truthy (Section 6.11.1) value
and it has been no shorter than the Minimum Interval since the last
execution, the Action is executed. When the Maximum Count of
executions is reached the TBR is disabled. The execution occurs
concurrently with any time processing and may take longer than the
Minimum Interval, so it is possible that multiple executions are
requested to overlap in time.
Each SBR has an enabled state to allow rules to be retained in an ADM
or ODM but not enabled during Manager-controlled time periods or
under certain Manager-desired conditions. See Section 4.3 for
details about what SBR-related controls are in the Agent ADM.
The definition of an SBR consists of the following:
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Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Action:
An SBR definition SHALL include an action in the form of a Macro
(MAC). When triggered, the action execution SHALL be executed in
accordance with Section 6.6 in an execution context with no
parameters.
Condition:
An SBR definition SHALL include a condition in the form of an
Expression (EXPR). The condition SHALL be evaluated in accordance
with Section 6.7 in an evaluation context with no parameters. The
result of the condition SHALL be converted to a BOOL value after
evaluation and used to determine when to execute the action of the
SBR.
Minimum Interval:
An SBR definition SHALL include a minimum execution interval in
the form of a non-negative TD value. The interval MAY be zero to
indicate that there is no minimum. This is _not_ a limit on the
interval of evaluations of the condition. This value can be used
to limit potentially high processing loads on an Agent.
Maximum Count:
An SBR definition SHALL include a maximum execution count in the
form of a non-negative UVAST value. The count sentinel value zero
SHALL be interpreted as having no maximum. This is _not_ a limit
on the number of evaluations of the condition.
Initial Enabled:
An SBR definition MAY include an initial value for its enabled
state. If not provided, the initial enabled state SHALL be true.
3.4.8. Time-Based Rule (TBR)
A Time-Based Rule (TBR) is a form of autonomy in which the Agent
performs an action at even intervals of time. The execution model of
the TBR is to start a timer at the Start Time of the TBR ticking at
an even Period; each time the timer expires the Action is executed.
When the Maximum Count of executions is reached the TBR is disabled.
The execution occurs concurrently with any time processing and may
take longer than the TBR Period, so it is possible that multiple
executions are requested to overlap in time.
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Each TBR has an enabled state to allow rules to be retained in an ADM
or ODM but not enabled during Manager-controlled time periods or
under certain Manager-desired conditions. See Section 4.3 for
details about what TBR-related controls are in the Agent ADM.
The definition of a TBR consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Action:
A TBR definition SHALL include an action in the form of a Macro
(MAC). When triggered, the action execution SHALL be executed in
accordance with Section 6.6 in an execution context with no
parameters.
Start Time:
A TBR definition SHALL include a start time in the form of a TIME
(Section 4.2.2) value. A relative start time SHALL be interpreted
relative to the absolute time at which the Agent is initialized
(for ADM rules) or the rule is created (for ODM rules). The start
time MAY be the relative time zero to indicate that the TBR is
always active. This is _not_ a limit on the interval of
evaluations of the condition.
Period:
A TBR definition SHALL include a period in the form of a positive
TD value. The period SHALL NOT be zero but any non-zero small
period is valid.
Maximum Count:
A TBR definition SHALL include a maximum execution count in the
form of a non-negative UVAST value. The count sentinel value zero
SHALL be interpreted as having no maximum. This is _not_ a limit
on the number of evaluations of the condition.
Initial Enabled:
A TBR definition MAY include an initial value for its enabled
state. If not provided, the initial enabled state SHALL be true.
3.4.9. Variable (VAR)
A Variable (VAR) is a stateful store of a value in an Agent. The use
of a VAR is similar to an EDD (Section 3.4.3) except that all the
behavior of a VAR is entirely within an Agent, while the ultimate
source of an EDD value is outside of the Agent.
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The value production of a VAR into a value SHALL be nilpotent and
have no side-effects in the processor.
The value produced by an VAR is allowed to, but not required to,
change over time. Because VARs can be referenced by condition
expressions of Time-Based Rules (Section 3.4.8) or elsewhere, an
Agent implementation could be optimized by allowing a VAR to indicate
when its produced value _would_ change. It is an implementation
matter for if and how an application can provide that indication.
A VAR has an initializer, which is used at Agent initialization and
to reset the VAR (see Section 4.3), but the VAR is otherwise stateful
and will retain its last value between any actions which modify it.
The definition of a VAR consists of the following:
Name, Enumeration, Status, Reference, Description:
As defined in Common Object Fields.
Parameters:
A VAR definition MAY include ARI parameters to be used when the
VAR is evaluated. Parameterized objects are discussed in
Section 7. Parameters for a VAR are only meaningful when the VAR
contains a value with actual parameters themselves containing a
LABEL value.
Type:
An VAR definition SHALL include the data type of the value
produced during evaluation, as described in Section 3.3. The type
of a VAR is fixed and SHALL NOT change between ADM revisions.
Initializer:
An VAR definition MAY include an initializer in the form of an
Expression (EXPR). The only times the initializer are evaluated
are at Agent Initialization and when a CTRL is used to reset the
state of the VAR.
| NOTE: It is possible to specify an expression that evaluates to
| a type different than the VAR itself. For example, if an EXPR
| adds two single-precision floating point numbers, the VAR MAY
| have an integer type associated with it. The VAR
| initialization will always be cast (Section 6.11) to the type
| of the VAR before assignment.
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4. Application Data Models (ADMs)
An ADM is a logical entity for defining static AMM object instances,
which are discussed in detail in Section 3.4. Each ADM exists as a
separate namespace for its contained objects, but allows importing
object _names_ from other ADMs to reuse them. Each Agent can support
any number of ADMs at one time (subject to implementation
limitations) and each Manager can operate with ADMs of different
revisions to support diverse Agents.
The following subsections define what is present in an ADM generally
and what objects necessary to operate a DTNMA Agent are present in
two base ADMs.
4.1. ADM Definitions
An ADM is "static" in the sense that it is revision-controlled and a
released revision of an ADM does not change. Besides AMM object
definitions there are metadata and handling rules for the ADM itself,
which are discussed in this section.
4.1.1. ADM Metadata
This section explains the purposes of the metadata fields of an ADM,
while the specific syntax for how these fields fit into an ADM module
is left to another document.
Name:
Each ADM definition SHALL contain a name field. An ADM's name
SHALL NOT change between ADM revisions. The name SHALL conform to
the id-text ABNF symbol of Section 4 of [I-D.ietf-dtn-ari].
Enumeration:
An ADM enumeration is an integer associated with the object, which
identifies the object just like its name. ADM enumerations
provide a stable and concise identifier for the binary encoded
form of an ARI. Each ADM definition SHALL contain an enumeration
field. An ADM's enumeration SHALL NOT change between ADM
revisions. The enumeration SHALL be an unsigned integer value.
Revision History:
Each ADM SHALL contain a history of dated revisions. At least one
revision SHALL be present and mark the date at which the ADM was
released for use. During development and testing an ADM need not
have updated revisions, only when a release occurs should a
revision be added.
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Status:
Each ADM definition SHOULD contain a status field. The valid
status value of an ADM SHALL be identical to the Status field of
YANG Section 7.21.2 of [RFC7950]. In the absence of a status
field, the status of the ADM SHALL be considered the same as the
status of the ADM which contains it.
Reference:
Each ADM definition SHOULD contain a reference field. A reference
is a text string referring to a specification or other document
which details the source or purpose of the ADM.
Description:
Each ADM definition SHOULD contain a description field. A
description is a text string explaining the purpose or usage of
the ADM in a human-readable format.
Features:
Each ADM definition MAY contain a set of feature definitions, see
Section 4.1.2 for details. Each feature SHALL have a name that is
unique within the namespace of the ADM. Each name SHALL conform
to the id-text ABNF symbol of Section 4 of [I-D.ietf-dtn-ari].
4.1.2. Features and Conformance
Following in the pattern of YANG features Section 5.6.2 of [RFC7950]
and SMIv2 conformance groups [RFC2580], the AMM has the concept of
ADM features and Agent conformance to those features. Each feature
is a simple qualified name and each object in an ADM can be
conditional on the conformance to a set of features.
4.2. Contents of a DTNMA ADM
The base DTNMA ADM is a necessary part of the AMM typing, execution,
and evaluation models. Rather than having some Agent logic defined
purely by specification, this document uses an "AMM" ADM to define
semantic types and controls needed for normal Agent operations. The
needed types are still set by specification and are unchanging within
an ADM revision, but this avoids having a separate, intermediate
typing system between the AMM-defined semantic types and the ARI-
defined literal types. This is also in-line with how YANG [RFC6991]
and SMIv2 [RFC2578] both rely on base modules for some core behavior.
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4.2.1. Simple Semantic Types
The most basic use of a semantic type is to provide additional
meaning to simple types. None of these types associates a unit with
the value, which it is expected that a derived type or an anonymous
type (at the point of use) would add for additional clarity.
These are summarized below:
counter32 and counter64: An unsigned integer value with an arbitrary
initial value which increments over time and wraps around the
maximum value. These correspond with the same names defined in
YANG [RFC6991] and SMIv2 [RFC2578].
gauge32 and gauge64: An integer value sampling some measurement
which can increase or decrease arbitrarily over time. These
correspond with the same names defined in YANG [RFC6991] and SMIv2
[RFC2578].
timestamp: An absolute time at which an event happened. This
corresponds with the same name defined in YANG [RFC6991] and SMIv2
[RFC2578].
4.2.2. Type Unions
All of the literal types defined in [I-D.ietf-dtn-ari] have a flat
structure, with some types sharing the same CBOR primitive encoding
but using distinct built-in type code points to distinguish them. In
order to allow types to fit into a more logical taxonomy, the AMM ADM
defines some specific semantic typedefs to group literal types.
These groups are not a strict logical hierarchy and are intended only
to simplify the effort of an ADM designer when choosing type
signatures.
These are summarized below:
TYPE-REF: The union of ARITYPE and TYPEDEF types.
INTEGER: The union of BYTE, UINT, INT, UVAST, and VAST types.
FLOAT: The union of REAL32 and REAL64 types.
NUMERIC: The union of INTEGER and FLOAT types.
PRIMITIVE: The union of NULL, BOOL, NUMERIC, TEXTSTR, and BYTESTR
types.
TIME: The union of TP and TD types.
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SIMPLE: The union of PRIMITIVE, and TIME types.
ANY: The union of LITERAL and OBJECT value-class types (Table 4).
This matches all values that can be in an ARI.
VALUE-OBJ: The union of CONST, EDD, and VAR reference types. This
matches any reference to an object that can produce a value
(Section 6.5).
NONCE: The union of BYTESTR, UINT64, and NULL types. This is used
to correlate Agent-Manager messages.
4.2.3. Expression (EXPR)
An Expression (EXPR) is an ordered collection of references to
Operators or operands. An EXPR takes the form of a semantic typedef
refining an AC to be a list of ARIs referencing OPERs, ARIs
referencing evaluate-able objects (see Section 6.7), or literal value
ARIs (with Simple Types). These operands and operators form a
mathematical expression that is used to compute a resulting value.
The evaluation procedure of an EXPR is defined in Section 6.7.
Expressions are used within an ADM for defining the initializer of a
Variable (VAR) and for defining the condition of a State-Based Rule
(SBR).
Since the Expression is an AC, there are no annotative constructs
such as parenthesis to enforce certain orders of operation. To
preserve an unambiguous calculation of values, the ARIs that form an
Expression MUST be represented in postfix order. Postfix notation
requires no additional symbols to enforce precedence, always results
in a more efficient encoding, and post-fix engines can be implemented
efficiently in embedded systems.
For example, the infix expression A * (B * C) is represented as the
postfix A B C * *.
4.2.4. Macro (MAC)
A Macro (MAC) is an ordered collection of references to Controls or
other Macros. A Macro takes the form of a semantic typedef refining
an AC to be a list of ARIs referencing Controls or objects which
produce other Macros.
The execution procedure of an MAC is defined in Section 6.6. Macros
are used within an ADM for defining the action of a State-Based Rule
(SBR) or Time-Based Rule (TBR).
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In cases where a Macro references another Macro, Agent
implementations MUST implement some mechanism for preventing infinite
recursions, such as defining maximum nesting levels, performing Macro
inspection, and/or enforcing maximum execution times.
4.2.5. Report Template (RPTT)
A Report Template (RPTT) is an ordered list of object references or
expression values used as a source for generating items for report
(Section 3.2.2.5) containers. A RPTT takes the form of a semantic
typedef refining an AC to be a list of references to value-producing
objects (VALUE-OBJ (Section 4.2.2)) or expressions (EXPR
(Section 4.2.3)). An object which produces an RPTT can itself be
parameterized so that the object flows down parameters as described
in Section 3.1.2.1.
A RPTT can be viewed as a schema that defines how to generate and
interpret a Report; they contain no direct values. RPTT values
either defined in an ADM or configured between Managers and Agents in
an ODM. Reports themselves are ephemeral and represented within ARI
built-in type RPTSET, not as part of the AMM object model. The
procedure for reporting on a RPTT is defined in Section 6.8.1.
RPTT values SHOULD be used within a CONST where possible. RPTT
values MAY be used within a VAR where necessary. This makes
correlating a RPT value with its associated RPTT easier over time.
Rather than having a VAR object's RPTT value changing over time, it
is RECOMMENDED to deprecate earlier RPTT-producing CONST objects and
create new objects.
4.2.6. Execution Target Type
A convenience typedef exec-tgt is defined to codify the type of
values allowed to be used as input for an Execution (or within an
Execution-Set (EXECSET) value) or produced by objects referenced as
execution targets. The execution target type is defined to be either
a direct CTRL reference, a direct MAC value, or a reference to a
value-producing object which itself is typed as exec-tgt.
4.2.7. Evaluation Target Type
A convenience typedef eval-tgt is defined to codify the type of
values allowed to be used as input for an Evaluation activity or
produced by objects referenced as evaluation targets. The execution
target type is defined to be either a direct SIMPLE value, a direct
EXPR value, or a reference to a value-producing object which itself
is typed as eval-tgt.
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4.3. Contents of an Agent ADM
While the DTNMA ADM described in Section 4.2 contains definitions of
static aspects of the AMM, the DTNMA Agent ADM is needed to include
necessary dynamic aspects of the operation of an Agent. This
separation is also helpful in order to allow the dynamic behaviors of
an Agent to be modified over time while the AMM definitions stay
stable and unchanging.
4.3.1. Agent State Introspection
The Agent ADM contains the following EDD objects used to introspect
the Agent's state, all of which can change over time within an Agent.
* The ADMs supported by the Agent, including the unique name and
revision of each. By indicating specific revision and supported
feature set, the contained objects in each ADM can be derived.
Because of this, the ADM-contained objects do not require
additional introspection.
* The set of SBRs and TBRs in the Agent's ODMs, along with controls
to ensure a specific object is either present or absent. These
are all conditioned on whether the Agent actually supports the
built-in rule feature.
* The set of VARs in the Agent's ODMs, along with controls to ensure
a specific object is either present or absent.
* Visibility into the execution state(s) of an Agent, including
counters for the total number of successful and failed executions.
* Counters for the total number of messages sent or received by the
agent, including reception failures.
4.3.2. Macro Helper Controls
The Agent ADM contains a set of controls which implement behaviors to
macro execution logic.
Branching Control: This control has a condition parameter to
evaluate and two optional parameters to define sub-macros, one of
which is executed depending upon the condition result truthy-ness.
Failure Catching Control: This control has one parameter of a macro
to execute normally and a second parameter of a macro to execute
on the condition that the normal execution fails for some reason.
Waiting Controls: This family of controls is to be embedded at the
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start (or anywhere within) a macro and pauses execution to wait on
either: a specific absolute time, a relative time from start-of-
control, or a condition to evaluate to truthy.
4.3.3. Basic Operators
The Agent ADM contains a set of operators which provide logical and
mathematical functions to macro execution.
Numeric Operators: These perform operations related to negation,
addition, subtraction, multiplication, division, and remainder
(modulo) of their operands. These perform numeric promotion of
their operands in accordance with Section 6.11.2.1.
Boolean Operators: These perform operations related to boolean NOT,
AND, OR, and XOR of their operands. These perform boolean casting
of their operands in accordance with Section 6.11.1.
Bitwise Operators: These perform bitwise NOT, AND, OR, and XOR
operations on only unsigned integer operands.
Comparison Operators: These perform pairwise comparison between
their operands. Equality and inequality can be performed on any
operand types, but ordered comparison (_e.g._, greater than) can
only be performed on numeric operands.
Table Filtering: This operator is used to process tables produced
within an expression to filter by row contents and specific
columns. This is an example of a parameterized operator because
the parameters control the filtering while the operand is the
table-to-be-filtered.
5. Operational Data Models (ODMs)
An ODM is a logical entity for containing AMM objects, similar to an
ADM (Section 4) but in an ODM the objects are not static. An ODM's
objects can be added, removed, and (with some restrictions) modified
during the runtime of an Agent. Like an ADM, each ODM exists as a
separate namespace for its contained objects and an Agent can contain
any number of ODMs.
Some object types, those which require implementation outside of the
Agent proper, are not available to be created in an ODM. These
include the CTRL, EDD, and OPER.
The actions for inspecting and manipulating the contents of an ODM
are available through EDDs and CTRLs of the Agent ADM
(Section 4.3.1).
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6. Processing Activities
This section discusses logic and requirements for processing of AMM
objects and values. Each subsection is a separate class of
processing that is performed by an Agent.
A Manager (or any other entity) MAY perform some of the same
processing, _e.g._ evaluating an expression, in order to validate
values or configurations before sending them to an Agent. That kind
of behavior is effectively creating a "digital twin" of the managed
Agent to ensure that the processing will behave as expected before it
is sent. For this reason, the subject noun used in all of these
activities is the "processor".
6.1. Agent Initialization
The initialization of the Agent state can be associated with a power-
on event or, due to the use of volatile memory, can be an explicit
activity initiated from outside the Agent runtime. If volatile
memory is used the contents of the ODMs on an Agent will be present
for the initialization procedure; otherwise the ODMs will be
considered empty or absent.
The procedure to initialize an Agent is as follows:
1. All ADM-defined VAR objects SHALL have their value set to one of
the following:
* If an Initializer is defined for the VAR, the value is the
result of evaluating the associated Initializer expression and
then converting (Section 6.11) to the VAR type.
* Otherwise, the value is undefined.
Any ODM-defined VAR objects MAY retain their state.
2. All ADM-defined TBR and SBR objects SHALL have their Enabled
state set to the Initial Enabled value. Any ODM-defined TBR and
SBR objects MAY retain their Enabled state. Any rules which are
enabled are ready for processing.
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6.2. ARI Resolving
Within an ADM, ARIs present in the various fields of object
definitions are URI References, which can take the form of Relative
URIs (see Section 4.2 of [RFC3986]). Any ARIs within an ADM
definition SHALL be handled as URI References and resolved in
accordance with the procedure of Section 5 of [RFC3986] with the
following used as a Base URI:
* For ARIs within a single AMM object definition, the non-
parameterized ARI of that object SHALL be the Base URI. This
includes ARIs used in nested structures under the object
definition; the object is the anchor point.
* For all other ARIs, the default Base URI ari:/ SHALL be the Base
URI. This means that all ARIs within an ADM _do not_ require a
URI scheme part.
6.3. Dereferencing
An Object Reference Values contains an object path and a parameter
part. Dereferencing an OBJECT value uses the object path to look up
a specific defined object available to the agent.
The process of dereferencing a value is as follows:
1. The value has to contain an object reference. If the value is
not an object reference, this procedure stops and is considered
failed.
2. The OBJECT value namespace (whether text or enumeration) is used
to search for a defined ADM or ODM namespace. A text form
namespace SHALL be compared within the UTF-8 character set in
accordance with [RFC3629]. An integer namespace SHALL be
compared numerically. If no corresponding namespace is
available, this procedure stops and is considered failed.
3. Within the namespace the object type and object name (whether
text or enumeration) is used to search for a specific defined
object. A text form object name SHALL be compared within the
UTF-8 character set in accordance with [RFC3629]. An integer
object name namespace SHALL be compared numerically. If no
corresponding object is available, this procedure stops and is
considered failed.
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6.4. Parameter Handling
An Object Reference Values contains an object path and a parameter
part. The parameter part of an OBJECT value represents the given
parameters (Section 3.1.2.1) being used. The given parameters are
present either as a (possibly empty) ARI list or an ARI map. Due to
nuances of the AMM value system, the given parameters are not
themselves either AC or AM values but similar to untyped ARI values.
The process to validate and normalize _given parameters_ against an
object's _formal parameters_ to produce _actual parameters_ is as
follows.
1. For each formal parameter, the processor performs the following:
If the given parameters are a list, the formal parameter is
correlated to the list by its position in the formal parameters
list. If the given parameters list does not contain a
corresponding position the given parameter is treated as the
undefined value. If the last formal parameter is a Sequence
(Section 3.3.7), it can correlate with multiple given parameters.
If the given parameters are a map, the formal parameter is
correlated to a map key by either its position (as an integer) or
its name (as a text string) but not both. If both integer and
name are present in the given parameters map the procedure stops
and is considered failed. If the given parameters map does not
contain a corresponding key the given parameter is treated as the
undefined value.
2. If any of the given parameters is not correlated with a formal
parameter the procedure stops and is considered failed.
3. For each correlated pair of formal parameter and given
parameter(s), the processor performs the following:
a. If the given parameter is undefined (whether explicitly or
implicitly) and the formal parameter defines a default value,
that default is used as the actual parameter value. If there
is no default value, the actual parameter is left as the
undefined value.
b. If the given parameter is a TYPEDEF and the object reference
itself has a parameter, the given parameter is treated as the
result of a type conversion (Section 6.11.3) to the semantic
type of the TYPEDEF. If the conversion fails this procedure
stops and is considered failed.
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c. The given parameter is converted to an actual parameter using
the type of the formal parameter in accordance with
Section 6.11. If the conversion fails, this procedure stops
and is considered failed.
| The TYPEDEF conversion behavior in step 3.b acts as an explicit
| type cast within a given parameter which allows explicit tie-
| breaking for type unions in the corresponding formal parameter.
The actual parameters resulting from this procedure are intended to
be able to be looked up by an implementation either by ordinal
position in the formal parameters list or by unique name of the
formal parameter. It is an implementation matter whether or not to
provide both accessing methods and the specifics of how, for example,
and EDD or CTRL runtime accesses actual parameter values.
An implementation MAY perform deferred "lazy" processing of any of
the above steps, causing a failure when the actual parameter value is
needed. One caveat about deferred processing is that it will not
fail if the parameter is unused, which is not necessarily a problem
but could mask other issues in whatever provided the given
parameters.
6.5. Value Production
Value production can be thought of as a common behavior used for
Execution, Evaluation, and Reporting activities. Within the AMM the
following entities have a value production procedure: CONST, EDD, and
VAR object references.
This activity relies on an object reference value to have been
dereferenced in accordance with Section 6.3 and its parameters
handled in accordance with Section 6.4. After that, each of the
object types is treated differently as defined in the following
subsections.
6.5.1. CONST and VAR Objects
Both CONST and VAR objects act as a store of a single literal value
within the Agent. Formal parameters on either CONST or VAR objects
are applicable only when the objects store a value which itself
contains parameters with at least one LABEL type.
The value production for these objects takes the stored value from
the object and augments it by label substitution based on the
following:
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1. The processor identifies all LABEL type within the stored value,
descending into container (Section 3.2.2) contents and object
reference parameter contents as necessary.
2. If any LABEL text is not present in the formal parameters of the
value-producing object then this procedure stops and is
considered failed.
3. For each LABEL value the corresponding actual parameter is not
the undefined value, the LABEL value is replaced by the actual
parameter.
This augmentation has no effect on the stored value, it occurs only
in the produced value. It is valid both for an actual parameter to
have no substitution occur with its value and for an undefined actual
value not be sued in substitution.
6.5.2. EDD Objects
For EDD objects, the actual parameters are used by the underlying
implementation to produce the value in an arbitrary way. The
produced value is typically either a SIMPLE (Section 4.2.2) value or
an ARI Table (Section 3.2.2.3).
The value production for these objects occurs outside of the Agent
proper within an implementation of the EDD being produced from.
The context given to the implementation is the following:
Object Identity:
This gives visibility into the EDD value which was dereferenced
during the production.
Actual Parameters:
The set of actual parameters used for the production.
Result Type and Storage:
The result of the production is placed here before completion.
The initial state of the Result Storage is the undefined value. It
is an implementation matter and author consideration (Section 7) to
enforce that the produced value is consistent with the type of the
object.
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6.6. Execution
Within the AMM only two entities can be the target of an execution
procedure: controls and macros. Controls are executed by reference,
while macros are executed both by value and by reference. This means
the execution target value SHALL match the exec-tgt (Section 4.2.6)
semantic type.
The procedure for executing is divided into phases to ensure that it
does not fail due to invalid references or produced values after some
controls have already been executed. The phases are processed as
follows:
1. In the expansion phase the target value is processed to
dereference all references, handle all parameters, and expand any
produced values.
If the target is a literal value, the following is performed:
a. The value needs to match the MAC (Section 4.2.4) semantic
type. If it does not match, this procedure stops and is
considered failed.
b. The processor then iterates through all elements of the MAC
value and performs the expansion step on each in turn. If
any sub-expansion fails, this procedure stops and is
considered failed.
If the target is an object reference, the following is performed:
a. The value is dereferenced in accordance with Section 6.3 and
its parameters are handled in accordance with Section 6.4.
If either fails, this procedure stops and is considered
failed.
b. If the target object is a value-producing object, a value is
produced in accordance with Section 6.5. This includes
substitution of any LABEL parameters within the value.
c. The processor then performs the expansion step on the
produced value. If sub-expansion fails, this procedure stops
and is considered failed.
After expansion the target is either a dereferenced CTRL object,
or a (possibly nested) macro expanded to contain only
dereferenced CTRL objects.
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2. The processor then executes the top-level expanded value as
either a macro in accordance with Section 6.6.1 or as a control
in accordance with Section 6.6.2
6.6.1. Expanded MAC Values
The execution of an Macro (MAC) value after expansion is as follows:
1. The processor iterates through all items of the expanded MAC in
order and performs the following:
If the item is an CTRL-REF it is executed in accordance with
Section 6.6.2. If the execution fails, this procedure stops and
is considered failed.
Otherwise the item is an expanded sub-macro and it is executed in
accordance with this procedure.
An effect of this procedure is that if any referenced CTRL fails
during execution the processing fails immediately and subsequent
CTRLs or MACs are not executed.
6.6.2. CTRL Objects
This activity relies on an object reference value to have been
dereferenced in accordance with Section 6.3 and its parameters
handled in accordance with Section 6.4.
The execution of a Control (CTRL) object occurs outside of the Agent
proper within an implementation of the CTRL behavior.
The context given to the implementation is the following:
Manager:
The manager which directly caused this execution, if available, is
provided as context.
Object Identity:
This gives visibility into the CTRL value which was dereferenced
during the execution.
Actual Parameters:
The set of actual parameters augmented for the execution.
Result Type and Storage:
The result of the execution is placed here before completion.
The initial state of the Result Storage is the null value.
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If the execution fails, the result value SHALL be treated as the
undefined value for the purposes of any subsequent reporting.
| The Agent ADM (Section 4.3) includes a wrapper CTRL "catch"
| which is used to ignore possible failures of specific
| executions and allow MAC processing to continue.
6.7. Evaluation
Within the AMM the following entities can be the target of an
evaluation procedure: references to value-producing objects, OPERs,
and TYPEDEFs and EXPR or SIMPLE literal values.
| For the purposes of these procedures, it is important to
| distinguish between an EXPR _value_ and a reference to a value-
| producing object which is typed to produce an EXPR value.
The procedure for evaluation is divided into phases to ensure that it
does not fail due to invalid references or produced values after some
expressions have already been evaluated. The phases are processed as
follows:
1. In the expansion phase the target value is processed to
dereference all references, handle all parameters, and expand any
produced values.
If the target is a literal value, the following is performed:
a. The value needs to match the SIMPLE (Section 4.2.2) or EXPR
(Section 4.2.4) semantic type. If it does not match, this
procedure stops and is considered failed.
b. If the value is an EXPR, the processor then iterates through
all elements of the EXPR value and performs the expansion
step on each in turn. If any sub-expansion fails, this
procedure stops and is considered failed.
If the target is an object reference, the following is performed:
a. The value is dereferenced in accordance with Section 6.3 and
its parameters are handled in accordance with Section 6.4.
If either fails, this procedure stops and is considered
failed.
b. If the target object is a value-producing object, a value is
produced in accordance with Section 6.5. This includes
substitution of any LABEL parameters within the value.
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c. The processor then performs the expansion step on the
produced value. If sub-expansion fails, this procedure stops
and is considered failed.
After expansion the target is either a SIMPLE value, or a
(possibly nested) expression expanded to contain only SIMPLE or
ARITYPE values, or dereferenced OPER or TYPEDEF objects.
2. If the expanded evaluation target is already a SIMPLE value, then
that is the result of the evaluation. Otherwise, the expanded
expression is evaluated in accordance with Section 6.7.1.
6.7.1. Expanded EXPR Values
The reduction of an Expression (EXPR) value after expansion is as
follows:
1. Any sub-expressions are first reduced to their result values
which are substituted back into the corresponding expression
item. If any sub-evaluation fails this procedure stops and is
considered failed. At this point the expression consists of only
SIMPLE or ARITYPEvalues, the result value of sub-expression
reduction, or dereferenced OPER or TYPEDEF objects.
2. An empty value stack is initialized for this reduction.
3. The expression is treated as a Reverse Polish Notation (RPN)
sequence, where the following is performed on each item in the AC
in sequence:
If the item is an ARITYPE value or dereferenced OPER or TYPEDEF
object it is evaluated in accordance with Section 6.7.4,
Section 6.7.2 or Section 6.7.3 respectively. If the evaluation
fails, this procedure stops and is considered failed.
Otherwise, the item is pushed onto the stack.
4. After RPN processing if the value stack is empty or has more than
one item, this procedure stops and is considered failed.
Otherwise, the result of the evaluation is the single literal
value in the stack.
One effect of this procedure is that if any referenced values cannot
be produced the procedure fails before any OPER is evaluated.
Another effect of this procedure is that if any referenced OPER fails
during evaluation or any value production fails the EXPR processing
fails immediately and subsequent OPER values, EXPR values, or VALUE-
OBJ references are not evaluated.
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6.7.2. OPER Objects
This procedure applies only during the evaluation of a containing
expression (Section 6.7.1); an OPER cannot be evaluated in isolation.
The evaluation of an OBJECT value referencing a Operator (OPER) is as
follows:
1. The processor verifies that the actual parameters, if any, are
consistent with the formal parameter associated with the OPER
being evaluated. If there is inconsistency, this procedure stops
and is considered failed.
2. The processor passes the evaluation on to the underlying
implementation of the OPER being evaluated.
The context available to the implementation is the following:
Object Identity:
This gives visibility into the OBJECT value which was
dereferenced during the evaluation.
Parameters:
The set of actual parameters augmented for the evaluation.
Expression Stack:
The operands are popped from this stack and the result is
pushed here before completion.
If the evaluation procedure fails, the failure SHALL propagate up to
any expression evaluation.
6.7.3. TYPEDEF Objects
This procedure applies only during the evaluation of a containing
expanded expression; a TYPEDEF object cannot be evaluated in
isolation. The evaluation of a TYPEDEF is handled similarly to a
unary OPER but it occurs entirely within the Agent and does not rely
on an object-specific implementation.
The evaluation of a TYPEDEF object is as follows:
1. If the TYPEDEF value itself has no parameters, the input value is
popped from the stack. If the TYPEDEF value itself has one
parameter, the input value is that parameter. If the TYPEDEF
value itself has more than parameter, this procedure stops and is
considered failed.
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2. The result value is a type conversion (Section 6.11.3) on the
input value. If the conversion fails this procedure stops and is
considered failed.
3. The result value is pushed onto the stack.
6.7.4. ARITYPE Values
This procedure applies only during the evaluation of a containing
expanded expression; an ARITYPE value cannot be evaluated in
isolation. The evaluation of an ARITYPE is handled similarly to a
TYPEDEF but with no possibility of a parameterized conversion.
The evaluation of an ARITYPE value is as follows:
1. The input value is popped from the stack.
2. The result value is a type conversion (Section 6.11) on the input
value. If the conversion fails this procedure stops and is
considered failed.
3. The result value is pushed onto the stack.
6.8. Reporting
Within the AMM the following entities have a reporting context: RPTT
and EXPR values and CONST, EDD, and VAR objects. The value-producing
objects are reported-on by reference, while RPTT are reported-on both
by value and by reference.
6.8.1. RPTT Values
The reporting on a Report Template (RPTT) value, which is structured
as an AC, is as follows:
1. An empty item list is initialized for this template.
2. The processor iterates through all items of the AC, performing
the following:
If the item is an EXPR value it is replaced by the result of
evaluation in accordance with Section 6.7. If the evaluation
fails the undefined value is used as a substitute.
Otherwise, if the item is a VALUE-OBJ it is replaced by the value
produced in accordance with Section 6.5. If the production fails
the undefined value is used as a substitute.
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Otherwise, the result of the production is the value appended to
the item list.
Because this procedure acts on an RPTT value and not an object
reference, the report itself cannot be assembled within this context.
One effect of this procedure is that if any item of the RPTT cannot
be reported on, the undefined value is used as a sentinel and the
other report items are still generated.
6.8.2. Value-Producing Objects
This activity relies on an object reference value to have been
dereferenced in accordance with Section 6.3 and its parameters
handled in accordance with Section 6.4.
The reporting on an object producing a value of any type is as
follows:
1. The value is produced from the object in accordance with
Section 6.5. This step includes substitution of any LABEL
parameters within the value.
2. If the value is an RPTT (Section 4.2.5) type, this value is used
to generate an AC which contains report items in accordance with
Section 6.8.1.
Otherwise, the produced value is used as the single RPT item.
3. The report (Section 3.2.2.5) is produced by combining: the source
ARI used for this procedure, the current timestamp, and the items
generated in the previous step.
6.9. Agent-Manager Message Handling
6.9.1. Execution-Set Aggregation
Managers SHOULD aggregate multiple Execution-Set (EXECSET) values
associated with the same Agent and Correlator Nonce into a single
Execution-Set. The aggregation MAY be based on a size limit (_e.g._,
number of targets), time limit, or an event (_e.g._, network
availability). This avoids the overhead of transport and processing
multiple executions on the same Agent, and due to the requirements in
Section 6.9.2 makes no difference to (lack of) guarantees in
execution order.
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6.9.2. Execution-Set Processing
An Agent SHALL process an Execution-Set through the independent
Execution of each item in the target list. Execution order is not
guaranteed and failures on one target do not affect other target, so
targets MAY be executed in any order or concurrently. This is not
the same behavior as the execution of a macro, where execution of
items is ordered and a failure of any execution causes subsequent
items to not be executed.
6.9.3. Reporting-Set Aggregation
Agents SHOULD aggregate multiple Reporting-Set (RPTSET) values
associated with the same Manager and Correlator Nonce into a single
Reporting-Set. The aggregation MAY be based on a size limit (_e.g._,
number of reports or number of total report items), time limit, or an
event (_e.g._, network availability or power-saving wake-up). This
avoids the overhead of transport and processing multiple messages on
a Manager and improves timestamp compression in the reports, but it
does require that all of the items are associated with the same
manager and nonce.
6.9.4. Reporting-Set Processing
A Manager SHALL process each report within a Reporting-Set
independently. Failures in processing any one report do not affect
other reports, so reports MAY be processed in any order or
concurrently. After using a Report Template to correlate report
items with source objects, a Manager SHALL treat each (timestamp,
object, item value) tuple independently from its containing
Reporting-Set or Report.
6.10. Type Matching
Type matching is done through pattern matching and does not affect
the AMM value. AMM values are not strictly typed, and as long as an
AMM value matches the pattern for a type, that value can be used
where that type is needed. If there is any overlap in the patterns
for different semantic types, then there will be ambiguity in the
sense that the same value can be used as different types.
6.10.1. Built-In Types
The matching of a built-in literal type to any object reference value
SHALL be considered to fail. The built-in LITERAL type SHALL match
any typed or untyped literal value.
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The matching of a built-in literal type to a typed literal value as
follows:
1. If the value type differs from the built-in type, the match
fails.
2. Otherwise, the literal type is matched to the value primitive as
defined below.
The matching of a built-in literal type to an untyped literal value
as follows:
NULL: This type only matches the null primitive value.
BOOL: This type only matches the true and false primitive values.
BYTE: This type only matches uint primitive values in the domain 0
to 2^8-1 inclusive.
INT: This type only matches int primitive values in the domain -2^31
to 2^31-1 inclusive.
UINT: This type only matches uint primitive values in the domain 0
to 2^32-1 inclusive.
VAST: This type only matches int primitive values in the domain
-2^63 to 2^63-1 inclusive.
UVAST: This type only matches uint primitive values in the domain 0
to 2^64-1 inclusive.
REAL32: This type only matches float primitive values in the domain
of a 32-bit [IEEE.754-2019] floating point number.
REAL64: This type only matches float primitive values in the domain
of a 64-bit [IEEE.754-2019] floating point number.
TEXTSTR: This type matches tstr primitive values.
BYTESTR: This type matches bstr primitive values.
TP: This type matches
// TBD values.
TD: This type matches
// TBD values.
LABEL: This type matches int and tstr values.
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CBOR: This type matches bstr primitive values.
ARITYPE: This type matches int and tstr values.
The matching of a built-in object reference type to any literal value
SHALL be considered to fail. The built-in OBJECT type SHALL match
any object reference values.
The matching of a built-in object reference type to an object
reference value SHALL be considered to succeed if the object
reference value Type ID is identical to the type.
6.10.2. Semantic Types
The matching of an input value to each class of semantic type
(Section 3.3) is as follows:
Named Type Use: Matching for a named type use SHALL be identical to
the matching for the type being named, whether that is TYPEDEF or
built-in.
Uniform List: Matching for this class SHALL require the value to be
an AC, with an item count optionally constrained by minimum and
maximum size from the type, and with each item of the AC itself
matching the specific sub-type for the list.
Diverse List: Matching for this class SHALL require the value to be
an AC, with an item count optionally constrained by minimum and
maximum size from the type, and with each item of the AC itself
matching the specific sub-type or sequence for the list.
Uniform Map: Matching for this class SHALL require the value to be
an AM, with a size optionally constrained by minimum and maximum
size from the type, and with each key and value of the AM itself
matching the specific respective sub-type for the map.
Table Template: Matching for this class SHALL require the value to
be an TBL, with a column count matching exactly the number of
columns present in the table template and each row containing
items matching the column-specific sub-type for the template. If
the table template contains a limit on minimum or maximum size,
the row count SHALL conform with those limits to match. If the
table template contains a key column or unique column-set then all
rows SHALL satisfy the uniqueness of those constraints to match.
Type Union: The matching for a type union SHALL be performed as
follows:
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1. The underlying literal types usable with a semantic type are
obtained by recursively flattening the type union(s) down to
built-in types and removing duplicate built-in types after the
first instance of them. This defines a list of acceptable
built-in types for the result.
2. The input value is matched to each built-in type in the list,
and the first successful match results in a success of
matching the whole semantic type. If none of the built-in
types can successfully match the input value, the match is
considered failed.
3. If successful, the specific base type which matched is also
part of the result of this procedure.
6.11. Type Conversion
The type system of the AMM allows conversions of values between
different literal and semantic types in a way which is supposed to
preserve the "meaning" of the value.
In some cases, type conversion is performed implicitly by the Agent
while other cases the conversion is explicitly part of an expression.
One example of implicit casting is during Parameter Handling to
ensure each processed parameter meets the formal parameter type
signature. Another example of implicit conversion is for numeric
operators in the Agent ADM (Section 4.3.3).
6.11.1. BOOL Type
The AMM has the concepts of "truthy" and "falsey" as being the result
of casting to BOOL type. Similar to the ToBoolean() function from
[ECMA-262], the AMM casting treats the following as falsey and every
other value as truthy:
* The undefined value
* The null value (of NULL)
* The false value (of BOOL)
* Zero value of BYTE, UINT, INT, UVAST, and VAST
* Positive and negative zero, and NaN values of REAL32 and REAL64
* Empty value of TEXTSTR and BYTESTR
* Zero value of TD
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When casting a value to BOOL type, the processor SHALL use the result
value false if the original value is falsey and true otherwise.
6.11.2. NUMERIC Types
The casting of a value to a NUMERIC type is intended to easily allow
mixed-type expressions while keeping the number of operators and
parameter unions small.
When casting a value to an INTEGER type from any other NUMERIC type,
the processor SHALL perform the following:
1. If the input is one of the FLOAT types and is not finite, the
conversion is considered failed.
2. If the input is one of the FLOAT types, the value is truncated to
an integer by rounding toward zero.
3. If the input value is outside the domain of the output type, the
conversion is considered failed.
When casting a value to an FLOAT type from any other NUMERIC type,
the processor SHALL perform the following:
1. If the input value is outside the domain of the output type, the
conversion is considered failed.
6.11.2.1. Numeric Promotion
While the earlier discussion of numeric type casting is about
converting from an input type to an output type, the concept of a
type promotion is about finding a "least compatible type" which can
accommodate most, if not all, of the input type range. Converting to
a promoted type is called an "up" conversion, and from a promoted
type a "down" conversion.
The promotion order for NUMERIC types is as follows:
* A promoted type has a larger span of values (the difference
between largest and smallest representable value).
* A promoted type can gain signed-ness but not lose it.
* A promoted type can lose precision for some values.
This promotion logic does not guarantee that an up-conversion will
always succeed (_e.g._ some large UVAST values will not fit within a
VAST or REAL32) but does provide a strict ordering for finding a
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compatible type between two NUMERIC values. The "least compatible
type" between two types SHALL be defined as the smallest up-
conversion that will accommodate the input types, as indicated in
Table 5. This is almost a strict ordering except for the conversion
of INT and UVAST to VAST to accommodate both the signed-ness and the
size of the inputs.
+========+======+======+=====+=======+======+========+========+
| | BYTE | UINT | INT | UVAST | VAST | REAL32 | REAL64 |
+========+======+======+=====+=======+======+========+========+
| BYTE | BYTE | UINT | INT | UVAST | VAST | REAL32 | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
| UINT | | UINT | INT | UVAST | VAST | REAL32 | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
| INT | | | INT | VAST | VAST | REAL32 | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
| UVAST | | | | UVAST | VAST | REAL32 | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
| VAST | | | | | VAST | REAL32 | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
| REAL32 | | | | | | REAL32 | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
| REAL64 | | | | | | | REAL64 |
+========+------+------+-----+-------+------+--------+--------+
Table 5: NUMERIC Type Promotion
6.11.3. Semantic Types
The converting of an input value to each class of semantic type
(Section 3.3) is as follows. Similar to built-in type conversion,
each semantic type class has the potential to change a value as
needed to conform to type limitations.
Named Type Use:
Uniform List: Converting to this class SHALL require the value to be
an AC; if the input is not an AC this procedure stops and is
considered failed. If the uniform list contains limits on the
number of items and the value does not satisfy those limits this
procedure stops and is considered failed. For each item of the
input value the uniform sub-type SHALL be used to convert to a
corresponding output value; if any of those conversions fail this
procedure stops and is considered failed.
Diverse List: Converting to this class SHALL require the value to be
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an AC; if the input is not an AC this procedure stops and is
considered failed. If the diverse list contains limits on the
number of items and the value does not satisfy those limits this
procedure stops and is considered failed. For each item of the
input value the corresponding diverse list sub-type SHALL be used
to convert to a corresponding output value; if any of those
conversions fail this procedure stops and is considered failed.
Uniform Map: Converting to this class SHALL require the value to be
an AM, if the input is not an AC this procedure stops and is
considered failed. If the uniform map contains limits on the
number of pairs and the value does not satisfy those limits this
procedure stops and is considered failed. For each key--value
pair of the input value the uniform sub-types SHALL be used to
convert to a corresponding output pair; if any of those
conversions fail this procedure stops and is considered failed.
If the conversion results in any duplicate keys this procedure
stops and is considered failed.
Table Template: Converting to this class SHALL require the value to
be a TBL, if the input is not an TBL this procedure stops and is
considered failed. If the table template contains limits on the
number of rows and the value does not satisfy those limits this
procedure stops and is considered failed. If the value contains a
different number of columns from the table template this procedure
stops and is considered failed. For each item across each row of
the input the corresponding column sub-type SHALL be used to
convert to a corresponding output table item; if any of those
conversions fail this procedure stops and is considered failed.
Type Union: Converting a value for a type union SHALL be performed
as follows:
1. The underlying built-in types usable with a semantic type are
obtained by recursively flattening type union(s) down to
built-in types and removing duplicate built-in types after the
first instance of them. This defines a priority list of
acceptable built-in types for the result. Because a TYPEDEF
union is unchanging within an ADM (see Section 3.4.2) a
processor MAY cache this flattened type list.
2. The input value is cast to each built-in type in the list, and
the first successful cast is taken as the built-in type of the
result value. If none of the built-in types can successfully
cast the input value, this procedure stops and is considered
failed.
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3. The result value is associated with the the type being cast
to, and that is the result of this procedure.
| Because the processing in Step 2 could successfully match
| multiple built-in types for an input value, the ordering of
| that list (and thus the ordering of the union members which
| flattened to produce that list) is significant.
6.12. Translating ARIs and Semantic Types
// NOTE: These procedures need to be validated by a trial
// implementation.
The procedures in this section allow AMM values, which can have a
semantic type (Section 3.3), to be translated into and out of the ARI
syntax (Section 3.1.3), which has no semantic type information. They
also describe a way to use type-less literal values to give further
compression of values in certain circumstances.
The compression of removing type information is possible only when
the context in which the value is being used has a specific semantic
or built-in type associated with it. For example, when a formal
object parameter or a report item is typed to either a built-in type
or a semantic type that doesn't represent a type union then a value
being used for the parameter or item can only have that specific
type; any other value type will be mismatched and invalid. Another
way of looking at this compression is when the value has the same
type as its context requires, then the value's type is redundant and
can be elided without loss of information.
In addition to compression by eliding semantic type within a context,
there are also some built-in types which have values which only exist
in that type. For example, the BOOL value true exists only within
that type while the UINT value 5 is also within the domain of INT and
several others.
For the procedures below, the contexts which provide type information
SHALL be: all formal parameters, VALUE-OBJ values, report template
items, tabular columns.
When translating from an AMM value into an ARI, the processor
performs the following:
1. If the use context is associated with a TYPEDEF and the value is
associated with an ambiguous or incompatible TYPEDEF, the ARI
form SHALL be wrapped in a TYPEDEF-as-cast ARI. An ambiguous
type is one where the presence of the inner type cast produces a
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different result than if the cast were absent. An incompatible
type is one where the presence of the inner cast results in a
failure of the outer cast.
2. If the use context is associated with a single built-in type (no
unions) and the built-in type is present in Table 2 "Literal
Implied Types" of [I-D.ietf-dtn-ari], the ARI form MAY have its
literal type removed.
When translating from an ARI into an AMM value, the processor
performs the following:
1. If the use context is associated with a type and the value is
associated with a different TYPEDEF or no TYPEDEF, the value
SHALL be cast to the context type in accordance with
Section 6.11.
7. ADM Author Considerations
The AMM model provides multiple ways to represent certain types of
data. This section provides informative guidance on how to express
application management constructs efficiently when authoring an ADM
document.
7.1. CTRL Definitions Need to Consider Idempotency
All CTRLs SHOULD be given names and behaviors that reflect the
idempotency requirements of Section 3.4.5. For example the term
"ensure" is preferable to "add or modify". Likewise "discard" is
encouraged instead of "remove if necessary".
Agent behavior SHOULD be reasonable even if duplicate and concurrent
CTRL executions are performed. Consider an "add_" CTRL that fails if
a value already exists as opposed to an "ensure_" CTRL that checks a
precondition and stops, thus guaranteeing idempotency.
7.2. EDD Definitions Need to Consider Nilpotency
All EDDs SHOULD be given names and behaviors that reflect the
nilpotency requirements of Section 3.4.3. Agent behavior SHOULD be
reasonable even if duplicate and concurrent EDD value production is
performed.
7.3. Use Parameters for Dynamic Information
Parameters provide a powerful mechanism for expressing associative
look-ups of EDD data. EDDs SHOULD be parameterized when the
definition of the EDD is dependent upon run-time information.
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For example, if requesting the number of bytes through a specific
endpoint, the construct num_bytes("endpoint_name") is simpler to
understand and more robust to new endpoint additions than attempting
to enumerate the number and name of potential endpoints when defining
the ADM.
7.4. Do Not Use Parameters for Static Information
Parameters incur transport and processing costs (see Section 6.4) and
should only be used where necessary. If an EDD object can be
parameterized, but the set of parameters is known and unchanging it
may be more efficient to define multiple non-parameterized EDD
objects instead.
For example, consider a single parameterized EDD object reporting the
number of bytes of data received for a specific, known set of
priorities and a request to report on those bytes for the "low",
"med", and "high" priorities. Below are two ways to represent these
data: using parameters and not using parameters.
+==============================+=============================+
| Parameterized Uses | Non-Parameterized Uses |
+==============================+=============================+
| ./EDD/num_bytes_by_pri(low) | ./EDD/num_bytes_by_low_pri |
+------------------------------+-----------------------------+
| ./EDD/num_bytes_by_pri(med) | ./EDD/num_bytes_by_med_pri |
+------------------------------+-----------------------------+
| ./EDD/num_bytes_by_pri(high) | ./EDD/num_bytes_by_high_pri |
+------------------------------+-----------------------------+
Table 6: Example Parameterized EDDs
The use of parameters in this case only incurs the overhead of type
checking, parameter encoding/decoding, and associative lookup. This
situation should be avoided when deciding when to parameterize AMM
objects.
7.5. Use Tables for Related Data
In cases where multiple EDD or VAR values are likely to be produced
and evaluated together, then that information SHOULD be placed in an
Table Template (Section 3.3.5) rather than defining multiple EDD and/
or VAR objects. By making a Table Template, the relationships among
various data values are preserved. Otherwise, Managers would need to
remember to query multiple EDD and/or VAR objects together which is
burdensome, but also results in increased transport and processor
utilization and the potential for non-synchronized access across
multiple value productions.
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8. IANA Considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of schema and namespaces
related to core ADMs, in accordance with BCP 26 [RFC1155].
8.1. DTN Management Architecture Parameters
This document relies on existing ARI-defined sub-registries defined
in [IANA-DTNMA] by Section 9.3 of [I-D.ietf-dtn-ari].
This document registers the following entries within the "Application
Data Models" sub-registry of the "DTN Management Architecture
Parameters" registry [IANA-DTNMA].
+=============+==================+=================+=======+
| Enumeration | Name | Reference | Notes |
+=============+==================+=================+=======+
| 1 | ietf-dtnma-agent | [This document] | |
+-------------+------------------+-----------------+-------+
Table 7: Application Data Models
9. Security Considerations
This document does not describe any on-the-wire encoding or other
messaging syntax. It is assumed that the exchange of AMM objects
between Agents and Managers occurs within the context of an
appropriate network environment.
The Access Control Lists (ACLs) functionality presented in this
document would be implemented separately from network security
mechanisms.
ACL groups are expected to be associated with Managers. However, the
form of Manager identification must be provided by separate
transport-specific ADMs. The AMM provides no general purpose
identifier, such as peer name and address, that would be required to
uniquely describe each Manager.
10. References
10.1. Normative References
[IANA-DTNMA]
IANA, "Delay-Tolerant Networking Management Architecture
(DTNMA) Parameters",
.
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[IEEE.754-2019]
IEEE, "IEEE Standard for Floating-Point Arithmetic",
IEEE IEEE 754-2019, DOI 10.1109/IEEESTD.2019.8766229, 18
July 2019, .
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, .
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
.
[I-D.ietf-dtn-ari]
Birrane, E. J., Annis, E., and B. Sipos, "DTNMA
Application Resource Identifier (ARI)", Work in Progress,
Internet-Draft, draft-ietf-dtn-ari-00, 22 February 2024,
.
10.2. Informative References
[ECMA-262] Ecma International, "ECMA-262 12th Edition, June 2021.
ECMAScript 2021 language specification", June 2021,
.
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[RFC1155] Rose, M. and K. McCloghrie, "Structure and identification
of management information for TCP/IP-based internets",
STD 16, RFC 1155, DOI 10.17487/RFC1155, May 1990,
.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578,
DOI 10.17487/RFC2578, April 1999,
.
[RFC2580] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Conformance Statements for SMIv2",
STD 58, RFC 2580, DOI 10.17487/RFC2580, April 1999,
.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, .
[I-D.ietf-dtn-dtnma]
Birrane, E. J., Heiner, S., and E. Annis, "DTN Management
Architecture", Work in Progress, Internet-Draft, draft-
ietf-dtn-dtnma-14, 28 April 2024,
.
Appendix A. Access Control Lists
This section presents an overview of fine-grained application
security using Access Control Lists (ACLs).
Access Control shall be a function of the Agent. A table of entries
associating permission tags with groups of objects shall be queried
at runtime to ensure privileged access, while simultaneously allowing
efficient implementation on an embedded device.
The concepts presented are in agreement with the Network
Configuration Access Control Model (NACM) documented in [RFC8341].
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A.1. Tags
Permissions are defined using an Access Control Tag (AT). Each AT is
a bit mask corresponding to a series of flags. For example three
bits would be required for read, write, and execute permissions.
Tags are similar in principle to file permissions on Unix, which
tracks flags for Read/Write/Execute.
An AT could be stored in a CBOR unsigned integer. For example 0x800C
would be a valid tag for an AT with four access controls of four bits
each.
A.2. Groups
Groups provide a general-purpose configuration to map an AT to a set
of objects.
An annotative name may be associated with a group, and a numeric
group ID is used for for cross-referencing.
A.2.1. Associations
The following entities within an Agent may retain group associations:
* The Agent shall be associated with a group.
* Each node in the network may have a group association. A
transport-specific ADM shall define how to map from authenticated
Manager identifier to an access control group.
* ADM objects shall be associated with the group of the Agent.
* ODM objects shall belong to the group associated with their
execution context of creation. This prevents a Manager from
exploiting permissions by, for example creating a one-second TBR
to execute a task requiring elevated permissions.
A CTRL is provided to allow an object's group to be re-assigned. If
a group is deleted all permissions associated with the group shall
also be deleted, and objects previously belonging to the group shall
inherit the default permissions.
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A.2.2. Permissions
Access control permissions shall be assigned using the combination of
a Group, ARI Pattern (defined in [I-D.ietf-dtn-ari]), and Access
Control Tag. At runtime the Agent shall retain a table of these
tuples to store all necessary permissions. The table shall be
queried by the Agent to find the corresponding AT for each managed
object. If an object does not have an AT in the table then the
default AT shall be used.
| NOTE: There are optimizations an implementation could do to
| avoid time-consuming table lookups, because an ACL will change
| infrequently and objects are added and removed at controlled
| points. For example: when an ADM implementation is loaded,
| when an ODM is modified, etc. Internally, the agent could
| associated access controls with an object and update object
| state as an ACL changes or when ACLs are being added.
The Agent shall use the Group corresponding to the appropriate
execution context when querying for permissions. For more
information see Appendix A.2.3.
An object's ARI shall be used by the Agent when querying the table.
An important consideration is that an ARI contains a namespace-id and
object-id, both of which may be expressed in either a text or numeric
form. When looking up permissions the Agent must use the ARI of the
object itself - which can match all four possible forms - and NOT
limit lookup to a particular ARI used by the Manager to reference an
object.
If the Agent discovers multiple tuples that correspond to an object,
the AT with least permission should be applied to the object. For
example, if three tuples would allow an operation and the fourth
would not, the Agent should deny permission.
Permissions shall be loaded during agent initialization and may be
changed by an operator with sufficient permission. The default
access level shall deny all operations.
An agent implementation should provide a way to audit assignment of
permissions.
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A.2.3. Execution Context
Each execution context shall be associated with a group. For direct
execution the group is expected to correspond to the Manager that
caused the execution to occur. For delayed execution such as a TBR
the execution context shall refer to the group of the applicable
object. When creating reports the ability to produce the report and
send to a Manager is driven by permissions of the group of the
Manager receiving the report.
// TBD There may be cases where an object is initialized as protected
but assigned to a variable that is not protected, allowing another
Manager a means of working around access controls. In this early
version of the document we do not protect against actions of a
malicious Agent, or a privileged manager abusing its privileges. An
Agent shall prevent an unprivileged Manager from abusing permissions
to perform an unprivileged action.
A.3. Enforcement
Access control shall be enforced in the following way for processing
activities described in Section 6.
A.3.1. Dereferencing
When a variable is dereferenced the Agent shall look up the AT
associated with the object. This is similar to other name-based
access control systems such as AppArmor in Linux.
A.3.2. Parameter Handling
Read permission shall be required for an object to be passed as a
parameter.
A.3.3. Value Production, Execution, and Evaluation
Execute permission shall be required for the object producing a
value, executing, or being evaluated. There is one exception: if an
OBJ-REF produces itself then Read permission is required.
Write permission is required for any object that could be modified by
an operation. Note that result storage is ephemeral and parameters
are passed by value, so any modifications to a VAR would be made by a
limited number of special CTRLs in the agent ADM such as store_var.
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A.3.4. Reporting
Read permission is required if the OBJ-REF is a single value that
will be reported directly.
Execute permission is required if the OBJ-REF is a RPTT that will be
used to generate a RPT.
A.4. Roles
Manager roles are implementation-specific and do not need to be
specified in the ADM. However the likely manger roles are Trusted
(all permissions) and Read-Only.
Acknowledgments
The following participants contributed technical material, use cases,
and useful thoughts on the overall approach captured in this
document: David Linko, Sarah Heiner, and Jenny Cao of the Johns
Hopkins University Applied Physics Laboratory.
Authors' Addresses
Edward J. Birrane, III
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723
United States of America
Phone: +1 443 778 7423
Email: Edward.Birrane@jhuapl.edu
Brian Sipos
The Johns Hopkins University Applied Physics Laboratory
Email: brian.sipos+ietf@gmail.com
Justin Ethier
The Johns Hopkins University Applied Physics Laboratory
Email: Justin.Ethier@jhuapl.edu
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