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RE: XML within XML - includes, transcludes, whatever

From: Smith, Ned <ned.smith@intel.com>
Date: Mon, 30 Oct 2000 09:18:19 -0800
Message-ID: <19BD7227A489D411AC5200902746200B0F8A35@orsmsx55.jf.intel.com>
To: "'Laird Popkin'" <laird@pop.mail.rcn.net>, xml-dist-app@w3.org
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I agree with Laird's observations that layering exists and should be
independent of one another. To that end, shouldn't this group make
some clearer statements relative to layering? What differentiates the
layers? How do different technologies (protocols, packaging, etc..)
interact within or across layers?

What are the layers? It seems to me there are three:
1) a messaging layer that is concerned with routing, addressing and
queuing; 
2) a packaging layer that describes the various forms of post
processing (compression, encryption, signing, cannonicalization, and
self-referential indexing (as in zip files or CID self-referencing); 
3) a document interchange layer which understands application
semantics of the various elements of the document. It enables
application integration because application data & semantics have
been normalized.

If XML is the right answer at each layer, then why - what properties
are important/relevant? 

What aspects of XML are overkill at the respective layers given their
properties?

Regards,
Ned.Smith@intel.com

- -----Original Message-----
From: Laird Popkin [mailto:laird@pop.mail.rcn.net]
Sent: Monday, October 30, 2000 1:41 AM
To: xml-dist-app@w3.org
Cc: laird@io.com
Subject: Re: XML within XML - includes, transcludes, whatever


It's an interesting document, but unless I misread it completely it
pretty
much said that you shouldn't *want* to wrap independent, validated
XML
within validated XML, since SGML, and thus XML, is meant to be used
within
one document with one DTD, and that instead what you should want to
do is
build the wrapped data by extending the wrapping DTD, or by not
validating.
Since SOAP (or any other general purpose XML-based protocol) requires
exactly this capability, either the article's assumptions don't apply
to us,
or we shouldn't be trying to use XML to build messaging layers. (I
also
think that DTD's and namespaces are meaningful, but that's a separate
discussion or two.)

Personally, I think that while SGML was intended purely to encode
individual
documents, XML has a broader application area, including use as a
messaging
protocol that can transport arbitrary content, including valid XML. I
admit
that I'm biased, in that I was part of a group (the ICE Authoring
Group)
that built a protocol using XML that does just that, that's been in
production for a few years, and in general XML has worked out very
nicely
for a whole raft of reasons that I am sure I don't need to elaborate
on
here. So rather than deciding that XML shouldn't be used for
messaging
protocols because this one issue is tricky, I'd prefer discussing
options
for doing so, within practical constraints. For example:

- - I don't think it's reasonable, or even desirable, to expect that
all
industry DTD's will be rewritten to be extensions of SOAP (or any
other
transport) -- the two layers should be independent.
- - I don't think it's reasonable to limit XML message payloads to
those that
do not include PCDATA.
- - I don't think that it's reasonable to require packaging all message
bodies
by reference, since that introduces a raft of serious security and
operational issues that are easily avoided by inline encoding in
cases where
that's appropriate.

Did I miss anything?

- ----- Original Message -----
From: "S. Mike Dierken" <mike@knownow.com>
To: <xml-dist-app@w3.org>
Sent: Tuesday, October 24, 2000 2:36 PM
Subject: RE: XML within XML - includes, transcludes, whatever


> Good document. Eliot can always explain things better and in more
> depth 
than
> I can.
>
> Mike
>
> > -----Original Message-----
> > From: xml-dist-app-request@w3.org
> > [mailto:xml-dist-app-request@w3.org]On Behalf Of Arjun Ray
> > Sent: Friday, October 06, 2000 11:25 PM
> > To: xml-dist-app@w3.org
> > Subject: Re: XML within XML - includes, transcludes, whatever
> >
> >
> > On Tue, 3 Oct 2000, S. Mike Dierken wrote:
> >
> > > [...] but XML already has an ID scoping mechanism - it is the
> > > 'document' concept. A document IS a scope.

This limitation is one of the reasons that ID's in XML aren't very
useful.

> > Wow!  I never thought that I would read this on a w3c list...
> >
> > > XML is a single document specification - it is a modular thing
> > > and multi-document concepts can be layered on top. There is no
> > > need to add more and more things into the base definition of
> > > XML. Many people have been using this internal-ref and
> > > external-ref approach for many years - just look at the Web.
> > [...]
> > > In short, I am against putting multi-document concepts into a
> > > single-document specification. There will always be a need to
> > > reference things outside the current document, and that
> > > mechanism is sufficient to deal with the problem.
> >
> > An echo from the past:
> >
> >
http://list.mc.duke.edu/scripts/WA.EXE?A2=ind9806&L=sgml-hl7&F=&S=&P=5
337
> >
> > (If the link doesn't work - they're having problems with the
> > server - <URL:http://www.nyct.net/~aray/notes/wek-namespaces.txt>
> > is a copy.) 
> >
> >
> > Arjun
> >
>



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Received on Monday, 30 October 2000 12:18:40 GMT

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