Adding Graph Transformation Concepts to UML's Constraint Language OCL

AbstractThe Object Constraint Language OCL is an integral part of UML, the Unified Modeling Language standard. It has been added to UML as a logic-based sublanguage for the definition of class invariants and pre-/postconditions of operations. OCL is rather similar to a subset of the graph transformation language PROGRES, the so-called path expressions. These path expressions are used for similar purposes as OCL. In contrast to OCL, path expressions support functional abstraction and offer additional operators for conditional iteration and transitive closure. Furthermore, PROGRES possesses a visual query sublanguage and is equipped with a precise semantics definition. Based on our experiences with the development of PROGRES a number of modifications and extensions of OCL are suggested as recommendations for its forthcoming version 2.0