XML Representation of Constraint Networks: Format XCSP 2.1

The Constraint Programming (CP) community suffers from the lack of a standardized representation of problem instances. This is the reason why we propose an XML representation of constraint networks. The Extensible Markup Language (XML) [18] is a simple and flexible text format playing an increasingly important role in the exchange of a wide variety of data on the Web. The objective of the XML representation is to ease the effort required to test and compare different algorithms by providing a common test-bed of constraint satisfaction instances. One should notice that the proposed representation is low-level. More precisely, for each instance, domains, variables, relations (if any), predicates (if any) and constraints are exhaustively defined. The current format should not be confused with powerful modelling language such as the high-level proposals dedicated to mathematical programming - e.g.