extensibility in XSchema?

Mark D. Anderson mda at discerning.com
Fri Jun 19 18:46:35 BST 1998

I hesitate to ask this question because (a) I haven't been
perusing either the discussion or the specs in detail, and
(b) I don't know SGML very well, which seems to be a
prerequisite to participation.

But I'd like some reassurance that when XSchema is done,
I will *not* ever have to parse comment structures to retrieve
metadata that the XSchema authors didn't choose to include
in a fixed repertoire of XSchema metadata declarations.

Currently, if I want to write a tool that helps users create
new instances from a schema, I've been using xml
to declare the "template", not a dtd, because I found it so
objectionable that I would have to read dtd comments to get
the information I wanted.

No fixed metadata will accomodate everything someone might want to know
about an element: suggestions for what GUI control to use for
entry and read-only reporting, a short and a long help text,
special validation regexps, complex conditional relationships
across elements, and so on.

Right now, writing a tool for creation of new xml documents
from only a dtd for information is like trying to write a 
database entry tool from only the rdbms-level schema information.
The information that a DTD provides is a joke, from the perspective
of an authoring tool.

There seems to be a constant undercurrent of religion in xml-dev
about validation vs. parsing vs. semantics, whose portent I
don't apprehend. The information necessary for validation is 
typically insufficient for an authoring tool. If the data 
structure can't accomodate the other information which the authoring
tool needs, then it will be left with putting information in
comments, or in some completely different file. 

I would expect that everything necessary for validation would
be an explicit part of XSchema, but that the schema for XSchema
itself (metametadata) would allow arbitrary elements in a valid
XSchema schema.


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