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   Re: [xml-dev] derivation by restriction and the use attribute

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"Helmut Dirtinger" <helmut_dirtinger@hotmail.com> writes:

> I am currently experimenting with derivation by restriction and
> attribute declarations. I tried all combinations of changing the
> attribute use="required|prohibited|optional" from the base type to
> the derivation.

The Schema REC [1] says the following on this question:

  2 For each attribute use (call this R) in the {attribute uses} the
    appropriate case among the following must be true:

    2.1 If there is an attribute use in the {attribute uses} of the
       {base type definition} (call this B) whose {attribute
       declaration} has the same {name} and {target namespace}, then all
       of the following must be true:
       2.1.1 one of the following must be true:
    B's {required} is false.
    R's {required} is true.

. . .

  3 For each attribute use in the {attribute uses} of the {base type
    definition} whose {required} is true, there must be an attribute
    use with an {attribute declaration} with the same {name} and
    {target namespace} as its {attribute declaration} in the
    {attribute uses} of the complex type definition itself whose
    {required} is true.

These constraints apply at the component level, so 'prohibited'
translates into no attribute at all.  Accordingly I read the allowed
cases as

       B        R

     required  required
     optional  required          [your case 2]
     optional  optional
     optional  [prohibited]      [your case 1]

> SQC grants three combinations: case 1 and 2 and a third one:
> (3) Basetype: use="required" Subtype:use="prohibited"

To my surprise, I find that SQC2.2 does indeed allow this case.  This
seems to me to be a mistake, as it violates clause (3) above.

> So my question concerns the validity of this third case. Is this
> case valid?

I don't think so.


[1] http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/#coss-ct
 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]


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