[Bug 11005] New: First note in 3.16.6.3 Type Derivation OK (simple)

http://www.w3.org/Bugs/Public/show_bug.cgi?id=11005

           Summary: First note in 3.16.6.3 Type Derivation OK (simple)
           Product: XML Schema
           Version: 1.1 only
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Datatypes: XSD Part 2
        AssignedTo: David_E3@VERIFONE.com
        ReportedBy: mike@saxonica.com
         QAContact: www-xml-schema-comments@w3.org
                CC: cmsmcq@blackmesatech.com


The Note in question reads: Note: It is a consequence of this requirement that
the value space, lexical space, and lexical mapping of D will be subsets of
those of B.

Two comments: 

(a) the indentation of the Note is curious. It is different from the
indentation of the immediately following notes, which suggests, I think
wrongly, that it is relevant only to the final clause of the constraint Type
Derivation OK (simple).

(b) I'm not sure that in the case of the lexical mapping, the Note is actually
true. Given a base type B defined as union(xs:string, xs:date), and the derived
type D defined as xs:date, then the lexical mapping for D includes the mapping
from 2010-10-10 to an xs:date, which is not present in the lexical mapping for
B (because that string maps to a value in the value space of xs:string).

(However, I'm having considerable trouble interpreting section 2.3 here. On the
one hand, it states that the lexical mapping for the type union(string, date)
is not a function, since the same string is the lexical representation of
values in both member types. On the other hand, the section says "Should a
derivation be made using a derivation mechanism that removes ·lexical
representations· from the·lexical space· to the extent that one or more values
cease to have any ·lexical representation·, then those values are dropped from
the ·value space·.", which, if it applies to union(string, date) would seem to
suggest that all dates are removed from the value space and therefore from the
lexical mapping; it's hard to reconcile these two statements.)

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Received on Sunday, 10 October 2010 22:47:25 UTC