Summary: In this paper, we present XOCL, an XML-based language to represent OCL (Object Constraint Language) constraints in UML models. XOCL was designed in two steps from the UML meta-model and OCL EBNF grammar published by OMG: (1) construction of a simple OCL meta-model and (2) derivation of an XML Schema for this meta-model. XOCL applications include full interoperability among UML modelling tools as well as finely grained structured input for automatic behavioral code generation and model checking.