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Bullard, Claude L (Len) wrote:
> Two only slightly related questions:
> 2. What are good reasons for having multiple schemas for the same
> instance?
This is something we're running into in the justice data model
effort (justicexml.gtri.gatech.edu). We have a fundamental
conflict between two schools:
1. Shared schema: This provides a common definition for syntax
and use of the data dictionary.
2. Document-specific schemas: These state document /
implementation-specific constraints on a document.
It's a fine line to walk. (1) is trying to solve the problem of
allowing machines to say things that can be understood, and (2)
is trying to prevent machines from saying things outside a
desired data space.
We've found that when attempting to apply document-specific
constraints, you pretty much have to throw out the concept of
common schemas and reused types. For example, if one part of a
document defines a type one way, another part of the document
can't define that type another way. And there seems to be no way
in XMLSchema to manage common / reusable schema components in
tandem with application-specific constraints.
One solution might be to disallow use of type-referencing in
instance documents (use of xsi:type=), and pass over instances
with validation against multiple schemas. That makes reuse of
global element definitions difficult, among other things.
We're starting to lean towards a solution like schematron for a
solution, but that steps away from the desired minimum toolset,
and requires a good bit of sophistication from the users.
Webb Roberts (webb.roberts@gtri.gatech.edu)
Research Scientist
Georgia Tech Research Institute
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