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[Bug 10236] key/keyref/unique fields having a complex type with simple content

From: <bugzilla@jessica.w3.org>
Date: Thu, 12 Aug 2010 23:41:37 +0000
To: www-xml-schema-comments@w3.org
Message-Id: <E1OjhOz-0007ou-TZ@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=10236





--- Comment #1 from C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com>  2010-08-12 23:41:36 ---
For the record (to save others the task of reconstructing this history from
scratch).

The crucial change seems to be in clause 3 of Validation Rule:
Identity-constraint Satisfied, which in 1.0 reads (in part):

  3 For each node in the ˇtarget node setˇ all of the {fields}, with that node
as the context node, 
    evaluate to either an empty node-set or a node-set with exactly one member,
which must 
    have a simple type. 

  http://www.w3.org/TR/xmlschema-1/#d0e13819

In the current public draft the corresponding sentence reads

  3 For each node in the ˇtarget node setˇ all of the {fields}, with that node
as the context node, 
    evaluates to a sequence of nodes (as defined in XPath Evaluation
(§3.13.4.2)) that only 
    contains ˇskippedˇ nodes and at most one node whose ˇgoverningˇ type
definition is either 
    a simple type definition or a complex type definition with {variety}
simple.

  http://www.w3.org/TR/xmlschema11-1/#sec-cvc-identity-constraint

Several change proposals are involved in this sentence; others appear nearby
but do not seem relevant to the point raised in the bug report.  In
chronological order, the changes appear to be:

  - modals (approved 18 February 2005), which changed "must have a simple type"
to
    "has a simple type" since there is already a "must" in the introductory
prose at 
    the beginning of the list.

  - idc (approved 17 November 2006), which was submitted to the WG in document
    http://www.w3.org/XML/Group/2004/06/xmlschema-1/structures.idc.200611.html
    and which is a fix to bug 1937 and bug 2219, which ask for clarification of
issues relating
    to the interaction of identity constraints with skipped subtrees and
xsi:nil='true'.

    Diff group idc changed 

        has a simple type

     to 

        either is ˇskippedˇ, or has [nil] true,  or has a ˇnon-absentˇ [schema
actual value].

  - idc1 (approved 1 December 2006), which contains amendments to the changes 
    adopted 17 November 2006 from an email sent by Sandy Gao on 21 Nov 2006
    http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2006Nov/0051.html

    In particular, the proposal adopted by the WG changed 

        evaluate to either an empty node-set or a node-set with exactly one
member, 
        which either is ˇskippedˇ, or has [nil] true, or has a ˇnon-absentˇ
[schema actual 
        value]

    to 

        evaluate to a node set that only contains ˇskippedˇ nodes and at most
one 
        node whose ˇgoverningˇ type definition is either a simple type
definition 
        or a complex type definition with {variety} simple.

  - b4416-3 (approved 3 August 2007), which changed 

        a node set

    to 

        a sequence of nodes (as defined in XPath Evaluation (§3.12.4))

It seems to me on first examination that the wording in question was introduced
by change idc1, but that the substantive change (of including elements whose
type is a complex type with simple content) was introduced by change idc and
the introduction of the phrase "non-absent [schema actual value]".

The minutes of 17 November and 1 December 2006 are at 

  http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2006Nov/0047.html
  http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2006Dec/0006.html

The latter notes in section 6.1.5:

    NM pointed out in email that there is a substantive change to allow both
simpletype 
    and complextype with simple content, but is now satisfied with the response
that 
    most developers already do it this way.

This appears to refer to the discussion thread started by SG's email cited
above.  In that thread, in turn, SG points to yet earlier discussions that have
a bearing here.

Schema comment R-206 ("pfiIdConstrFields: Can fields identity nodes with types
having simpleContent?"
http://www.w3.org/2001/05/xmlschema-rec-comments.html#pfiIdConstrFields,
migrated to Bugzilla in 2005 as bug 2198) directly raises the question at issue
here.  The issue (raised in February 2003) was discussed in the call of 29
August 2003:

  http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2003Sep/0002.html

The WG seems to have been of divided mind whether the text of 1.0 was clear and
needed a substantive change, or unclear and in need of a clarification.  A test
was constructed:

  http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2003Aug/0035.html

Empirical research showed that all of the then-available processors tested
(Tibco, Oracle C, Oracle Java, xsv, Xerces C, Xerces J) interpreted the rules
in the spec as covering (i.e. allowing) both simple types and complex types
with simple values.  The WG then reached the formal conclusion that the text of
1.0 was not clear, rather than that it was clear and said the wrong thing.  So
the official view of the WG (at least, the WG of 2003) is that the change at
issue here is not a substantive change but only a clarification.

>From the initial description of this issue, I infer that opinions may still be
divided on whether the 1.0 text is clear or not.  But in any case, I agree with
the implicit suggestion that this should probably be listed explicitly among
the changes, if we can find wording we can agree on.

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Received on Thursday, 12 August 2010 23:41:39 UTC

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