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   Re: Names and schemas

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  • From: Paul Prescod <papresco@technologist.com>
  • To: xml-dev@ic.ac.uk
  • Date: Mon, 01 Jun 1998 15:38:42 -0400

Tim Bray wrote:
> I don't really agree with Paul Prescod's argument that the current
> namespace draft invades schema turf.  It does state that presumably
> namespaces will in general have associated schemas (surely no-one here
> disagrees?), but it bends over backward to avoid relying on the existence,
> availability, or format of these schemas.  

Namespaces will, in general, also have associated stylesheets. Maybe in 10
years, they will, in general, also have associated Java classes and Yahoo
categories. I don't think that schemas should be separated out from all
other types of processing specifications. I especially don't think that we
should priviledge a view that says that every element should have a
*single* schema, which is the issue that really annoys the architectural
form people (and with good reason!).

> At the moment, based on some
> off-line experimentation, I do think that the namespace facility will
> lend itself quite elegantly to the construction of partial composable
> schemas, the need for which is not in doubt. -Tim

The namespace facility will also lend itself to the construction ofpartial
composable stylesheets, Java rendering specifications, and perhaps "Yahoo
ontology descriptions" (I made that one up). Once again, the separation
out of schemas just leads to confusion. 

Plus, the fundamental problem is in the very first line:

"We envision applications of Extensible Markup Language [XML] where a
document contains markup defined in multiple schemas"

Schemas do not define markup. If they did, then the idea of an element
type being constrained by multiple schemas at the same time would be
impossible. But it is not. Schemas constrain markup. Schemas define
classes of markup. Schemas do not define markup (or elements, or element
types). Even SGML never claimed that DTDs defined element types. I
consider this a fundamental error. SRCDEF is just the technical
manifestation of the error.

 Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

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