XML Representation of Constraint Networks: Format XCSP 2.1
  We propose a new extended format to represent constraint networks using XML.
This format allows us to represent constraints defined either in extension or
in intension. It also allows us to reference global constraints. Any instance
of the problems CSP (Constraint Satisfaction Problem), QCSP (Quantified CSP)
and WCSP (Weighted CSP) can be represented using this format.
