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[Bug 2048] R-182: clarify equality and identity of union values

From: <bugzilla@wiggum.w3.org>
Date: Thu, 08 Sep 2005 22:42:18 +0000
To: www-xml-schema-comments@w3.org
Message-Id: <E1EDV62-0005dN-OG@wiggum.w3.org>


           Summary: R-182:  clarify equality and identity of union values
           Product: XML Schema
           Version: 1.0
          Platform: PC
               URL: http://www.w3.org/2001/05/xmlschema-rec-
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XSD Part 2: Datatypes
        AssignedTo: cmsmcq@w3.org
        ReportedBy: cmsmcq@w3.org
         QAContact: www-xml-schema-comments@w3.org

[This was originally raised by Stefan Wachter and booked as
Rec comment R-182.  It's now being transferred to Bugzilla.}

A similar question (to that of R-181, see bug 2044)
concerning equality arises with union types. Having the two
union types:

  <simpleType name="u1">
    <union memberTypes="string"/>

  <simpleType name="u2">
    <union memberTypes="string"/>

are these two elements equal?

  <element xsi:type="u1">abc<element> 
  = <element xsi:type="u2">abc<element>


Response from Henry:

The Working Group discussed this issue at the May 2005 face
to face meeting and instructed the editors to prepare
wording proposals.  [The minutes do not explicitly say, but
the editors' recollection is, that the agreement was that
two unions may have overlapping value spaces, and that
equality of values is based on the identity of the value
(viewed as a member of a primitive datatype's value space),
not on the additional identity or structural similarity of
the datatypes whose value spaces it may be a member of.  In
other words, the two values in the example offered by Stefan
Wachter are identical.]

Note that we need both a 1.0 corrigendum and a wording
proposal for 1.1.  Because identity and equality are
distinct relations in 1.1 but not in 1.0, the wording
proposals will not necessarily be the same.  This
record is for the 1.0 corrigendum.
Received on Thursday, 8 September 2005 22:42:22 UTC

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