extensibility in XSchema?
SimonStL at classic.msn.com
Mon Jun 29 15:06:29 BST 1998
[It doesn't look like this made it to XML-Dev last night, so I'll try again.]
Where I'm going right now takes into account Friday's suggestions from Ron
Bourret, John Cowan, and Paul Prescod. Hopefully, the stew is a good one.
XSchema processors are only responsible for handling information in the XSC
namespace. Extensible information is going to involve more than our basic
framework provides. XSchema will provide this information with a home, and
make it available to applications, but this information will not be checked by
XSchema itself. Only the XSC namespace(i.e., core element/attribute)
information will be managed by the XSchema processor. This is sufficient for
creating DTDs from XSchemas, while providing room for all the other
information people need. (This is my response to Paul's suggestion that
XSchema processors only manage the XSC namespace.)
The contents of this metadata need to be standardized as well. XML-Data could
provide a start for this. I think it goes beyond the limited tasks we've set
ourselves, though it is certainly key to providing the functionality which
many people on this list clearly want. This could be XSchema 2.0, or we could
attempt to do it in 1.0, or it could be a separate spec.
Conformance is becoming more and more of an issue; sections 4.0 and 5.0
(XSchema->DTD and XSchema processing) will need to address this head-on. We
can't make apps conform to portions of the standard which aren't specified, of
Versioning will be implemented through namespaces as well - I'll figure out
the details on the src and ns URLs shortly. I'm pondering PURL/versionNumber.
XSchemas had been moving in a direction where simple validation was enough to
make sure the XSchema was properly structured. This is getting in the way of
several suggestions that could potentially improve XSchema, for instance Chris
Maden's reduction of the empty elements in the notation and attribute
declarations to attributes. The tasks that have been proposed for XSchema
processors are not very complex and provide significant improvements in
XSchema readability and authorability. I'm leaning more and more toward
giving XSchema processors a bit more work to do.
The impact of these decisions on the XSchema DTD is at present fairly small.
Unless I hear an uproar, many of the current empty elements will be moving to
an attribute-based model in the next revisions of the attribute declaration
and notation declarations. There will also be an ANY content model (PCDATA
seems too brutal) creeping into a space provided for non-XSC namespace
extensions. Namespaces do not appear to exempt elements from validation. I
would like XSchemas to be validatable if not governed by their validation.
John Cowan wrote:
>I think that both of these lose, and that UserSpecific is very ugly,
>et iterum censeo Carthago delenda est....
Carthago delenda est did come to an end with a peace treaty between the cities
of Rome and Carthage in 1985. Unfortunately, I don't see a much better
solution at present.
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