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Date: Fri, 4 Jan 2013 18:46:43 +0000
To: abnf-discuss@ietf.org
From: Paul Overell <paul@bayleaf.org.uk>
References: <20130103171755.20983.75939.idtracker@ietfa.amsl.com>
	<50E5BF59.9000207@alum.mit.edu> <50E5D4C5.8010800@alum.mit.edu>
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Subject: Re: [abnf-discuss] A proposal for adding import and scopping to ABNF
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Hi,

In message <50E5D4C5.8010800@alum.mit.edu>, Paul Kyzivat=20
<pkyzivat@alum.mit.edu> writes

I think this is a very interesting idea, to formalize import and export=20
of ABNF between documents.  Some thoughts, questions and quibbles:


1)

>       named-rulelist =3D
>          rulelist-name *WSP "{" rulelist "}" c-nl
>
>       rulelist-import =3D
>          (basic-import / named-import) c-nl

I think there is a minor problem with the syntax here, it doesn't allow=20
*WSP before the c-nl.  But be very careful when fixing this as the=20
original syntax contains some ambiguity concerning white space, which is=20
subject to an errata:=20
http://www.rfc-editor.org/errata_search.php?rfc=3D5234&rec_status=3D2&prese=
nt
ation=3Drecords.

2)

>   o  The <basic-import> simply inserts all the ABNF from the=20
>referenced
>      document.
>   o  The <named-import> is similar, but does the import within a new
>      <named-rulelist>.  This is just syntactic sugar, but is
>      convenient.  E.g. the following:
>
>       CORE@"urn:ietf:rfc:5234"
>
>      is equivalent to:
>
>       CORE {
>          @"urn:ietf:rfc:5234"
>       }

This doesn't seem to allow importing just a named-rulelist from another=20
document.  E.g if document 1 has
SYNTAX1 {
    doc1syntax1 =3D ...
}
SYNTAX2 {
    doc1syntax2 =3D ...
}

How do I specify in document 2 that I wish to import just SYNTAX1, and=20
not SYNTAX2?

The named-import seems to import ALL the ABNF from another document into=20
a new namespace - or have I misunderstood?

4)

Have you considered an import syntax to specify importing just a=20
specific rule or list of rules?  E.g. Importing from RFC5234 one might=20
just want some of the core rules from Appendix B, but not want the ABNF=20
Definition of ABNF in section 4.

5)

What are the semantics of importing a rulelist that itself imports a=20
rulelist?  Is circularity allowed (doc1 import from doc2, doc2 imports=20
from doc1)?  If so is a parser expected to detect circularity to avoid=20
an infinite loop?


Regards
--=20
Paul Overell

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