Automatically Binding Variables of Invariants to Violating Elements in an OCL-Aligned XBase-Language

Constraints that have to hold for all models of a modeling language are often specified as invariants using the Object Constraint Language (OCL). If violations of such invariants shall be documented or resolved in a software system, the exact model elements that violate these conditions have to be computed. OCL validation engines provide, however, only a single context element at which a check for a violated invariant originated.Therefore, the computation of elements that caused an invariant violation is often specified in addition to the invariant declaration with redundant information. These redundancies can make it hard to develop and maintain systems that document or resolve invariant violations. In this paper, we present an automated approach and tool for declaring and binding parameters of invariants to violating elements based on boolean invariant expressions that are similar to OCL invariants. The tool computes a transformed invariant that returns violating elements for each iterator variable of the invariant expression that matches an explicitly declared invariant parameter. The approach can be used for OCL invariants and all models of languages conforming to the MetaObject Facility (MOF) standard. We have evaluated our invariant language and transformation tool by transforming 88 invariants of the Unified Modeling Language (UML).