Defining proprietary XSD types (with semweb library)

I did a few searches and could not find a decent answer so posting here. Is there a way to be able to define proprietary xsd types…let’s say I want to define currency:us so that I can have a literal "12.0"^^currency:us. I want to be able to map that to say xsd:decimal and then let the semweb framework understand and treat it that way.