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RE: merge mode for XML

From: Peter Ring
Subject: RE: merge mode for XML
Date: Wed, 1 May 2002 22:31:47 +0200

I might just sit back and watch the show, but I like to be part of the
fun ;)

DTDs are certainly not enough in a lot of situations, and XML Schemas,
RELAX NG, or what-have-you won't ever obliviate the need for documentation
and project management.

But sometimes, well-formed XML is worthy of version management even
when no-one bothers about a schema. For example, you might need to save
some of those short-lived XML-formatted messages for a regression test.

Also, there is now a trend towards a more Unix-like 'tool-set' approach,
in which different parts of a chain of processes are responsible for
different tasks. While it might be valuable early in a proces to validate
an XML instance, it might be a waste of resources later in the proces.

There's also another interesting trend: HyTime is slowly being re-invented
in XML incarnation. Which to me is proof-of-concept: you can dream up
another syntax (and a full-blown SGML parser might even be able to parse
it, given a suitable SGML declaration), but in the end, it doesn't make
much of a difference whether you write <concept>something</concept> or
(concept something) or \concept{something} or whatever; the fundamental
issue is the same: You are not really supposed to look at the markup
except as an expression of structure.

Which was what started this thread: how to diff and merge in a meaningful
way, i.e. in a way that knows that <whatnot a="bar" b="foo" /> isn't
different from <whatnot   b="foo"   a="bar" /> in a way that most XML
applications should care about. You can come this far with just well-formed
XML. When it comes to whitespace in character context, things get really
interesting. XML in essence leaves it up to the application what to do with
whitespace, so you have to know the application in order to decide whether
a whitespace difference matter. A DTD or schema helps a lot because you
can then ignore whitespace in element context.

BTW, I stumbled over yet another XML diff, this one written by
Norman Walsh:

and a small feature about whitespace and prettyprinting XML:

Kind regards

Peter Ring

-----Original Message-----
From: address@hidden [mailto:address@hidden Behalf Of
Gary Bisaga
Sent: 1. maj 2002 17:12
To: CVS-II Discussion Mailing List
Subject: RE: merge mode for XML

Sorry, this strikes me as just a little bit extreme. I agree that you ought
to write DTDs or schemas (just yesterday I had to make one of our developers
do so, and our own internal XML infrastructure requires them). But to call
documents without DTDs/schemas "not XML" and unworthy of configuration
management is certainly not supported by the XML spec or common usage. For
one thing, as I'm sure you know, the XML spec does not seem to deprecate
well-formed XML documents. When I was in the W3 XML working group (1999)
there was certainly a group of us (not everybody) who believed that
well-formed documents had a place in the world.

And if we take this tack, what about constructs not declarable with DTDs?
XML Schemas will certainly improve this, but many people are not using them
yet. Are DTDs with "ANY" declarations also not XML, since they really don't
describe the semantics of the document? Since DTDs can't describe data types
or other restrictions (such as field length), is any DTD'ed document "not

DTDs and schemas are good and should be used wherever possible. But there
are realities of life.

<>< gary

-----Original Message-----
From: address@hidden [mailto:address@hidden Behalf Of
Greg A. Woods
Sent: Wednesday, May 01, 2002 1:56 AM
To: Peter Ring
Cc: CVS-II Discussion Mailing List
Subject: RE: merge mode for XML
> <rant>There's a class of simple XML documents that live and
> die without getting near either a DTD or revision control.
> Without a schema and accompanying documentation, there's no
> way to tell the semantics of the XML document, and not much
> point in version management.</rant>

Amen.  I couldn't agree more!
Those who dare call such things "XML" are sadly mistaken.

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