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Re: Problem with types derived from mixed complex types

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Sat, 05 Jun 2004 11:09:02 +0100
To: Tait E Larson <telarson@us.ibm.com>
Cc: "Michael Kay" <mhk@mhk.me.uk>, xmlschema-dev@w3.org
Message-ID: <f5bpt8e71vl.fsf@erasmus.inf.ed.ac.uk>

Tait E Larson <telarson@us.ibm.com> writes:

>       <xs:complexType name="BASE" mixed="true">
>             <xs:sequence>
>                   <xs:element name="elemA" type="xs:integer" />
>             </xs:sequence>
>             <xs:attribute name="attrB" type="xs:string" />
>       </xs:complexType>

> I get the following error when I try to validate this schema or the schema
> you provided:
>
>
> src-ct.2: Complex Type Definition Representation Error for type 'SUB'.
> When simpleContent is used, the base type must be a complexType whose
> content type is simple, or, only if extension is      specified, a simple
> type.

That error message is wrong, as Michael correctly pointed out by
reference to the revised REC.  But your example is _still_ not valid,
because your complex BASE is not *emptiable*.

The uncorrected REC contained a contradiction between clause 5.1.2 of
Derivation Valid (Restriction, Complex) [1] which said (and still
says, although it's now numbered as 5.2.2.2) if a complex type
definition derived from a base with complex has simple content:

  "The {base type definition} must be mixed and have a particle which
  is ·emptiable· as defined in Particle Emptiable (§3.9.6)."

So if elemA had minOccurs="0" you'd be OK.

The problem in the uncorrected REC was that it _also_ said, in the
definition of the mapping from schema documents to components for
Complex Type Definition[s] with simple content [2]:

  "if the type definition ·resolved· to by the ·actual value· of the
  base [attribute] is a complex type definition (whose own {content
  type} _must be a simple type definition, see below_) and the
  <restriction> alternative is chosen," [emphasis added]

This evidently contradicts the first quote.  The W3C XML Schema WG
decided to resolve the contradiction in favour of _allowing_ such
derivations.  Accordingly, E1-27 in the errata document [3] and the
Proposed Edited Recommendation [4] change the _second_ passage quoted
above and add an extra mapping clause to cover the relevant case:

  "1. If the type definition ·resolved· to by the ·actual value· of
  the base [attribute] is a complex type definition whose own {content
  type} is a simple type definition and the <restriction> alternative
  is chosen, . . .

  "2. If the type definition ·resolved· to by the ·actual value· of
  the base [attribute] is a complex type definition whose own {content
  type} is mixed and a particle which is ·emptiable·, as defined in
  Particle Emptiable (§3.9.6) and the <restriction> alternative is
  chosen, . . ."

Hope this helps clear things up,

ht

[1] http://www.w3.org/TR/xmlschema-1/#derivation-ok-restriction
[2] http://www.w3.org/TR/xmlschema-1/#Complex_Type_Definition_details
[3] http://www.w3.org/2001/05/xmlschema-errata.html#e1-27
[4] http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/#Complex_Type_Definition_details
-- 
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                     Half-time member of W3C Team
    2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
            Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                   URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]
Received on Saturday, 5 June 2004 06:09:16 GMT

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