Are people really using Identity constraints specified in XMLschema?

[Priti Patil <priti@dsl.serc.iisc.ernet.in>]

Hi all,

I am a research student. I am working on the project which will convert
identity constraints specified in XML schema to relational keys while
mapping XML to relations. 

As a curiosity to see, how important are the identity constraints from
the perspective of XML application developer, I thought that let me see
how many people are using XML schemas which has key, keyref. For that, I
surveyed the schemas which are provided in the repository of  XML.org.
But none of the schema contains the use of integrity constraints. 

Thus question which come into my mind is that Are people really using
Identity constraints specified in XML schema?

Can any one tell me answer to this?

Thanks and Regards,
Priti Patil.