[dsdl-discuss] Overlaying schema expressions

Hello all!

I tried to spark a discussion on XML-Dev regarding overlaying schema
expressions "on top of" normative schema expressions from other organizations:

   http://lists.xml.org/archives/xml-dev/200405/msg00313.html

... but no-one was interested in taking the bait and talking more about this.

I'm curious what people here think about this.

If an organization publishes a normative W3C Schema expression for a
document model, and I want to create a restricted subset whose instances
validate against the original document model, I feel I can keep the
namespace of the original vocabulary and just write a secondary set of
constraints that would be applied to a given document before or after, but
always in conjunction with, the normative schema expression.

Does this sit well with people, or is the act of creating a new document
model (the subset) obligating me to come up with a new namespace?

I don't want a new namespace because stylesheets and other processing
applications are namespace-sensitive and should be working with the subset
since an instance of the subset is an instance of the big schema.

Mechanically, I know I can do it, and in my post noted above I suggest
doing it either (1) with a relaxed set of non-typed elements and attributes
that solely validate the structure and used in conjunction with the
normative schema, or (2) with a rigourous set of typed constraints working
standalone and mimicking the normative schema but not being "official".

My gut feel is (1) is more politically palatable, non-threatening to the
original schema, and truer to the sense of "an additional set of
constraints developed by an outside organization for users of a particular
application or profile of a published normative schema maintained under the
auspices of its original owner".

But (2) is more technically palatable to tools such as editing tools that
are (understandably) designed to constrain information to a single
expression of constraints instead of combining multiple expressions of
constraints.

I'm leaning towards (1) and I'm curious what others have to say about
this. A big reason why (1) appeals to me is that I may have numerous
profiles and subsets I can describe with numerous non-typed
hierarchy-only-checking expressions, not having to worry about content data
types as I can just rely on the normative schema to provide the validation
of those aspects of the instance.

Thanks for any input you may have and for any discussion to follow.

........................ Ken

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