choosing elements based on attribute values

I use W3C schema 1.0. I need to make an element or set
of elements mandatory or optional based on the
attribute value as below:

<parent>
 <child age="10" sex="male">
    <property>
     <p1/>   
     <p2/>
     <p3/>
    <property>
    <property>
     <p1/>  //mandatory only if age=10, sex=male
     <p2/>
     <p3/>
    <property>
 </child>
 <child age="12" sex="female">
    <property>
     <p1/>   //mandatory only if age=10, sex=male
     <p2/>
     <p3/>
    <property>
 </child>
<parent>


How do I check the attribute values(age and sex) and
make element 'p1' mandatory or optional based on the
attr value?

I use w3c schema 1.0.

I downloaded the latest xmlspy. And it doesn't seem to
support XSD 1.1.

cheers!
dave




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