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See bug 2044 and bug 2045 for full description of the issue which gave rise to this one. When the Working Group discussed R-181 in May 2005 (North Carolina ftf), we instructed the editors "to correct validation rules for identity contraints to actually refer to identity." It's not clear to me, at the time I add this record, whether the instruction applies only to 1.1 or also to 1.0. Since equality and identity are the same in 1.0 but not in 1.1, I suspect there may be a need for two slightly different proposals. For now, though, I am concerned with fixes to the 1.1 text, so I'm entering this as a 1.1 issue. We can make a separate 1.0 issue if we wish, or change this to apply to 1.0 (which means it will implicitly also apply to 1.1).
On the call of 23 February 2007 the Working agreed to class this issue as editorial.
At the ftf meetings of October 2007, the XML Schema WG discussed this issue together with the XML Query and XSL WGs (in the context of a discussion of bug 3243). QT vigorously argued that the direction outlined for this issue in the comments on bug 2045 and bug 2046 should be reversed and that XSDL should align with QT in treating the difference between atomic values and singleton lists containing those atomic values as a purely metaphysical distinction. After discussion, we agreed to instruct the editors to prepare wording proposals for Datatypes (bug 2046) and structures (bug 2047), in which it's made clear that for XSDL purposes singleton lists are not distinguished from the atomic values which are their list items. As far as we could tell, this would affect only identity constraints, since we couldn't think of any way to construct an enumeration or a fixed value constraint which would involve comparison of an atomic to a singleton list. (Further thought shows that a union of a pattern-restricted integer with a list of differently pattern-restricted integers would allow tests to be constructed.) These wording proposals will, we hope, be useful in achieving agreement on the correct technical direction. (That is, they are phase-1 proposals, not phase-2 proposals.) Before we make any final decisions, we should perform some due diligence to see if existing processors all do the same thing in these cases (and what that thing is) and whether existing schemas seem likely to be affected.
A wording proposal intended to resolve this issue is now at http://www.w3.org/XML/Group/2004/06/xmlschema-1/structures.b2047.html (member-only link). It should probably be read in conjunction with its companion proposal for Datatypes at http://www.w3.org/XML/Group/2004/06/xmlschema-2/datatypes.b2046.html (member-only link)
The proposals mentioned in comment #3 were adopted by the WG on today's call. Accordingly I am marking the issue resolved. The originator of the issue, Stefan Wachter, has been notified by email and asked for his feedback.