> Given an XML such as this:
> <data>
> <documents>
>   <document id="1"/>
>   <document id="2"/>
> </documents>
> <persons>
>   <person>
>         <name>Chris</name>
> 	<document relid="4"/>
> 	<document relid="7"/>
>   </person>
>   <person>
>         <name>John</name>
> 	<document relid="2"/>
>   </person>
> </persons>
> </data>
> 
> I want to list all people 

/data/person

who *have* documents 

/data/person[document]

but do *not* have at least one document that is in the <documents> list.

/data/person[document][not(document/@relid = /data/documents/@id)]

Michael Kay
http://www.saxonica.com/