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Re: Data Model(s) for XML 1.0 / XML Devcon / DOM / XSL / Query

• From: Robin Cover <robin@i...>
• To: "W. E. Perry" <wperry@f...>
• Date: Fri, 23 Feb 2001 11:57:41 -0600 (CST)

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 "pre-ordained".

What are the "expected pre-ordained semantics"
in the following document, and in what way do
these semantics tyrranize anyone?

<?xml version="1.0" ?>
<!DOCTYPE Jjhgdf [
<!ELEMENT Jjhgdf (wemnr | wkjhrn | sdbfs)* >
<!ATTLIST Jjhgdf IFdfj CDATA #IMPLIED >
<!ELEMENT wemnr (#PCDATA) >
<!ELEMENT wkjhrn (#PCDATA) >
<!ELEMENT sdbfs (#PCDATA) > ]>
<Jjhgdf IFdfj="348-kdf 'sugob' dfjg">
<sdbfs>kjewr</sdbfs>
<wemnr>rwejk</wemnr>
</Jjhgdf>

Ditto for the SGML variant with "- -" in
element type declarations.

Does the DTD induce you to infer in this
instance that a "Jjhgdf" of the real world contains
a "sdbfs"?  No.  XML has no concept of "contains."
Does the DTD induce or require you to infer in this
instance that a "wemnr" of the real world
"follows" a "sdbfs"?  No.  XML has no concept
of "follows", in any world, real or unreal.

What DTD "semantics" are you protesting?

Robin Cover

-------------------------------------------------------------

On Fri, 23 Feb 2001, W. E. Perry wrote:

> Sean McGrath wrote:
> 
> > In the light of recent debate about the intertwingling
> > of XML specs and the PSVI and Henry Thomsons
> > excellent keynote at XML Devcon
> > (http://www.xml.com/pub/a/2001/02/21/xmldevcon1.html).
> >
> > isn't it time to accept that not specifying formal
> > post-parse data model(s) for XML 1.0 was a big
> > mistake?
> 
> In a word, no. Those post-parse plus post-additional-processing data
> models are in effect being specified now by, among others, the very
> groups whose work you cite here. Some of us, however, regard (and need)
> XML as a lightweight syntax cleanly separated from the specifics of the
> processing--and therefore separated from the instance local semantics
> which will be derived--at every node where an XML instance document is
> put to use. IMH (if oft expressed) personal opinion, the great
> innovation and original value of XML is the concept of well-formedness.
> By permitting an instance document to stand on its own as syntax,
> without the expected pre-ordained semantics expressed in a DTD (or for
> that matter, in any form of content model, schema, or canonical
> 'infoset'), XML took the decisive step which SGML never had.
> Well-formedness recognizes that an instance document will be processed
> afresh by every user of it, and implicitly recognizes that the needs,
> and therefore the processing required, will be different for each one.
> The simplest processing of every document is well-formedness syntax
> checking. In some few cases that will be all the processing required.
> Beyond that first pass of process, it may be necessary in particular
> cases to check a document for conformance to a content model or data
> schema; to transform it to some other document form; to elaborate from
> it an infoset; or not.
> 
> The decision of which of those processes to apply, in what order, and
> with what interactions among them is a profoundly local decision, driven
> by uniquely local expectations and needs. Simon St.Laurent, among
> others, has repeatedly drawn attention to these interactions and asked
> for, at a minimum, recognition of them, if not a packaging or processing
> model to mediate their effects. The current debate on re-inventing
> XPath/XSLT as XQuery is premised on the same questions of how the
> various officially 'recommended' processes are supposed to defer to, or
> otherwise interact with, one another. My answer to that is seditious,
> but awfully useful in designing locally necessary processing:  beyond
> well-formedness, W3C specifications in the XML family are often the
> right tools for implementing required processes, but are certainly not
> the only tools available. Every processing node requires a fresh design
> because the results required at each node, and the XML documents and
> other data available to it to work with, are different. At a minimum,
> the order of processes needs to be carefully examined and uniquely
> specified for each node, if only to control the interactions among them
> in a predictable and appropriate way. Those interactions can never be
> known in the abstract or general case:  they are the result of specific
> instance data in a particular processing environment. It is my
> suggestion that we design for that reality--using the tools in each case
> most suitable--rather than attempt a grand unification of semantics
> which are by their very nature utterly local.
> 
> Respectfully,
> 
> Walter Perry
> 
> 
> 
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