Help on AttributeDesingator!

Hi 
All!

 

   Its 
said that attribute designator takes the instance in the request context and 
that will be used to match under say subject/resource match based on the 
designator rt ?. I am not sure how the node is picked in here 
?

 

<SubjectMatch
 MatchId="urn:oasis:names:tc:xacml:1.0:function:rfc822Name-match">
<AttributeValue
 DataType="http://www.w3.org/2001/XMLSchema#string">
 med.example.com
</AttributeValue>
<SubjectAttributeDesignator
 AttributeId="urn:oasis:names:tc:xacml:1.0:subject:subject-id"
 DataType="urn:oasis:names:tc:xacml:1.0:data-type:rfc822Name"/>
</SubjectMatch>

 

so when the request 
context is received will it pick the subject id from the request and then 
compare it with this i.e med.example.com ?

 

Thanks

Balaji Kamal 
Kannadassan