Hi Michael,

I think the only way to do that is to have two separate attributes - one 
that refers to the book and the other that contains the page number.  If you 
created a list of a union of IDREF and string it would never validate the 
reference because something like "yourbook" will always be a valid string.

Hope that helps,
Priscilla

------------------------------------------------------------------
Priscilla Walmsley
Author, Definitive XML Schema  /  XML in Office 2003
http://www.datypic.com
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"Michael Möllney" <m.moellney@i...> wrote in message 
news:u5wW%23QOKGHA.3876@T......
> Hi Group....
>
> I'm looking for a XML Schema description that validates an aggregation of 
> an ID in an attribute:
>
> XML looks like
>
> <BOOK id="mybook" />
> <CHAPTER name="Chap1" page="mybook:23" />  // should be valid
> <CHAPTER name="Chap2" page="mybook:40" />  // should be valid
> <CHAPTER name="Chap3" page="yourbook:65" />  // fail: no ID 'yourbook'
>
> where id in BOOK is an ID type
> and
> where page in CHAPTER should be validated to be of pattern: 
> IDREF':'string.
>
> I did not find a way to describe this....
> If this is easy, please point me to a description for this....
> I could only find how to produce lists of atomic types.
>
> So probably I could somehow produce a list (using space instead of ':' as 
> separator) of unions containing IDREF and string but is there a nicer way?
>
> Any help would be fine,
> thanks in advance,
>
> Michael