Modular Embedding of the Object Constraint Language into a Programming Language

The Object Constraint Language (OCL) is a well-accepted ingredient in model-driven engineering and accompanying modeling languages like UML (Unified Modeling Language) or EMF (Eclipse Modeling Framework) which support object-oriented software development. Among various possibilities, OCL offers the formulation of state invariants and operation contracts in form of preand postconditions. With OCL, side effect free query operations can be implemented. However, for operations changing the system state an implementation cannot be given within OCL. In order to fill this gap, this paper proposes the language SOIL (Simple OCL-like Imperative Language). The expression sub-language of SOIL is identical to OCL. SOIL adds well-known, traditional imperative constructs. Thus by employing OCL and SOIL, it is possible to describe any operation in a declarative way and in an operational way on the modeling level without going into the details of a conventional programming language. In contrast to other similar approaches, the embedding of OCL into SOIL is done in a new, careful way so that elementary properties in OCL are preserved (for example, commutativity of logical conjunction). The paper discusses the central principles behind this conservative embedding of OCL into SOIL. SOIL has a sound formal semantics and is implemented in the UML and OCL tool USE (UML-based Specification Environment).