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Re: Specifying integrity constraints on type

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 24 Aug 2001 11:45:07 +0100
To: Guillaume Rousse <rousse@ccr.jussieu.fr>
Cc: xmlschema-dev@w3.org
Message-ID: <f5bpu9lenyk.fsf@cogsci.ed.ac.uk>
Guillaume Rousse <rousse@ccr.jussieu.fr> writes:

> Hello.
> I got some problems defining correct xpath expression for some identity 
> constraints in a XML schema, where the enclosing element name is not 
> constant.
> 
> I have a generic EventType type:
> <complexType name="EventType" abstract="yes">
>   <sequence>
>     <element name="author" minOccurs="1" maxOccurs="unbounded">
>       <complexType>
>         <attribute name="idref" type="string" use="required"/>
>       </complexType>
>     </element>
>   </sequence>
> </complexType>
> 
> I want to ensure an author could only be a person, so i have a key for 
> persons defined in my root element:
> <key name="personKey">
>   <selector xpath="persons/person"/>
>   <field xpath="@id"/>
> </key>
> 
> And the corresponding keyref will be something as:
> <keyref name="eventAuthor" refer="personKey">
>   <selector xpath="?"/>
>   <field xpath="@idref"/>
> </keyref>
>
> But now, how must i define the xpath attribute for the selector element, so 
> as to match only author element from an event type ? As this last one is a 
> type, it can occurs with arbitrary name (aka identification, observation, 
> etc...)...

Until XPath 2.0, which I expect will allow you to match on types
explicitly, the best you can do is

  xpath='.//author'

> Auxiliary question: key definition make key field mandatory. Does keyref 
> definition makes keyref fields mandatory also ?

Yes.

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
Received on Friday, 24 August 2001 06:44:44 GMT

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