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RE: Data Model(s) for XML 1.0 / XML Devcon / DOM / XSL / Query
- From: "Bullard, Claude L (Len)" <firstname.lastname@example.org>
- To: "W. E. Perry" <email@example.com>, XML DEV <firstname.lastname@example.org>
- Date: Fri, 23 Feb 2001 15:22:19 -0600
I think you get this, Walter, but let me make sure I do.
The problem is, the instance (XML UTF/ASCII file)
does NOT contain the same information as the
real "instance" (struct, object, table) pick one)).
The data actually being processed once the
document is past the well-formed parse is subject
to alteration. For example, namespace processing
adds information. DTD processing adds information.
Other processes such as XSLT transforms, XPath
slicing and dicing, XQuery LETs, etc. operate not
against XML, but against that post-parser data
structure. (This isn't new: SGML DTD processing
added information too, (#FIXED) and we blithely
said "the software handles this" and by gum,
some did, some didn't, who knew. It was truly
messy to buy an SGML system as a result.)
TODAY: per XML 1.0, we don't have a common model
for what is in there. In other words, a node
IS-Not A Node per the properties the node has.
In the grove world, they would say the original
grove was not completely specified, so the grove
plans for each process are noisy or simply, invalid.
The Grove guys were right; just hard to grok.
That makes it pretty hard to do something like
XML Query because there is no way to ensure two
implementations have the same data if they come
from two different upstream processors. The ONLY
thing one can count on is the XML UTF file and
that is just BagOCharacters.
To do more than move bags, we need a common
data model. So far so good. Question: given
the rate of specs coming out, how many MORE
PVSI processes will be spec'd and will they
force us to loop back again? Before the
XML community really takes Henry to heart here,
let's ask that question and see if we think
we have a reasonable answer. Minimal victory
solutions are MORE costly if the next step
is a loopback.
Ekam sat.h, Vipraah bahudhaa vadanti.
Daamyata. Datta. Dayadhvam.h
From: W. E. Perry [mailto:email@example.com]
Sent: Friday, February 23, 2001 2:40 PM
To: XML DEV
Subject: Re: Data Model(s) for XML 1.0 / XML Devcon / DOM / XSL / Query
Robin Cover wrote:
> Hmmm... You wrote:
> > By permitting an instance document to stand on
> > its own as syntax, without the expected pre-ordained
> > semantics expressed in a DTD.. XML took the decisive
> > step which SGML never had
> I don't understand, unless something is lurking in "expected" and/or in
What is lurking is the 'pre' in "pre-ordained" (which implies 'expected').
nothing is expected, then it is legitimate to consider only the body of the
instance document. If a content model or schema is desirable as a means to
describe the document structurally, generically, or abstractly, then it can
derived from the instance.