VO-DML subsetting

[Laurent Michel]

Hello,

In my model, I would like to put a constraint (SubsettedRole) on an attribute value in the context of a specific class:

Example:
   - SuperClass A(attribute: a:string)
   - SubClass B extends A (constraint: a='ImB')

This is legal in UML since constraints are free text but the VO-DML validator (schematron) disallow this.
The Schematron validates constraints by applying a regular expression on the SubsettedRole which reject any sort of expression:

   [a-zA-Z][a-zA-Z0-9\._\-]+:[a-zA-Z][a-zA-Z0-9\._]*

This is fine to put a constraint on class name (Class B extends A (constraint: a is instance of X)) , but nothing in the spec 
disallows to write an expression like (Class B extends A (a is not null))

How can I do this?

Laurent
-- 
jesuischarlie/Tunis/Paris/Bruxelles/Berlin

Laurent Michel
SSC XMM-Newton
Tél : +33 (0)3 68 85 24 37
Fax : +33 (0)3 )3 68 85 24 32
Université de Strasbourg <http://www.unistra.fr>
Observatoire Astronomique
11 Rue de l'Université
F - 67200 Strasbourg