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Re: SOAP's prohibiting use of XML internal subset

From: Mark Nottingham <mnot@mnot.net>
Date: Mon, 25 Nov 2002 14:15:06 -0800
Message-ID: <055501c294d0$42692290$f4457743@mnotlaptop>
To: "Tim Bray" <tbray@textuality.com>, "Paul Grosso" <pgrosso@arbortext.com>
Cc: <www-tag@w3.org>

>  I think the Web Services community ought
> to be real nervous about flying in the face of an IETF BCP.

Why? It's a Best Current Practice, and it is explicitly scoped to use of
XML within *IETF* protocols. It's just that community's best current
thinking (words directly from RFC2026) on a particular topic, and may
(dare I say probably will) change.

Granted, if there is a desire to make it possible to use Web services as
the basis of IETF protocols, there might be cause for concern; however,
that isn't a requirement that I've heard for a while, and I imagine that
the IETF isn't terribly inclined to start using them willy-nilly either;
Web services have a different audience.

Also, at first glance, the logic in that document seems to be faulty; it
says one shouldn't impose "additional restrictions beyond those imposed by
the XML recommendation itself" because "an implementer of the protocol may
not be able to use an otherwise conforming XML processor to parse the
XML-based protocol elements."

If they are truly restrictions, how could a conformant processor not be
able to parse the result? I grant that a vanilla conforming generator
*may* have difficulty, depending on the abstraction that it presents to
the programmer.

> - On the other hand, I think it's entirely reasonable that SOAP agents
> be forbidden from being required or expected or even allowed to charge
> off fetching DTDs or external parameter entities at run times, for
> obvious performance and security reasons.

This gets to the heart of the question, I think; can specific applications
of XML restrict the use of syntactic mechanisms it defines? Your answer
seems to be a conditional "yes."

However, I don't think it's supportable to be selective, at least at this

> - That granted, forbidding an internal subset seems kind of dumb.
> Speaking as an XML processor implementor, the extra code required is
> hardly detectable and the performance gain not significiant.
> Furthermore, every XML processor in the world just silently does the
> internal subset and it's going to cost *extra work* for SOAP
> implementations to check that they haven't.  I.e. you can't use an
> ordinary off-the-shelf non-validating XML processor.

Perhaps the WG has a good reason for this prohibition; have they been
Received on Monday, 25 November 2002 17:16:45 UTC

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