[Bug 4517] Why forbid value constraints on ID types?

http://www.w3.org/Bugs/Public/show_bug.cgi?id=4517

           Summary: Why forbid value constraints on ID types?
           Product: XML Schema
           Version: 1.1 only
          Platform: Macintosh
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Structures: XSD Part 1
        AssignedTo: cmsmcq@w3.org
        ReportedBy: cmsmcq@w3.org
         QAContact: www-xml-schema-comments@w3.org


Clause 3 of Schema Component Constraint: Attribute Declaration 
Properties Correct reads:

    3 If the {type definition} is or is constructed from ID, 
      then there is no {value constraint}.

Similarly, clause 5 of Schema Component Constraint: Element Declaration 
Properties Correct reads: 

    5 If the {type definition} or {type definition}'s 
      {content type}'s {simple type definition} is or is 
      constructed from ID, then there is no {value constraint}.

These are, I think, holdovers from the past: they reconstruct constraints
originally formulated for SGML DTDs and carried over for compatibility
reasons to XML 1.0 and 1.1 DTDs.  But they violate the principle of
orthogonality: why should value constraints be allowed for some types
but forbidden for others?

The spec becomes simpler and the design cleaner if these ad hoc
rules are dropped.  The WG's decision on bug 4348 reflects the view
that compatibility with the ID-related constraints of SGML and
XML DTDs no longer needs to be a high-priority goal.  I believe we
should remove these unhelpful constraints.

Received on Wednesday, 2 May 2007 01:52:38 UTC