Dale,
Conceptually looks good.
Interoperability details/aspects.
With:
<xsd:attributeGroup name="pullAttributes">
<xsd:attribute name="mpc" type="xsd:anyURI" use="optional"/>
<xsd:anyAttribute namespace="##other" processContents="lax"/>
</xsd:attributeGroup>
I guess you don't know what parameters go with the mpc URI.
Do we want to leave it that open ended though?
Thanks, DW