A Formal Framework for Viewpoint Consistency

Multiple Viewpoint models of system development are becoming increasingly important. Each viewpoint offers a different perspective on the target system and system development involves parallel refinement of the multiple views. Viewpoints related approaches have been considered in a number of different guises by a spectrum of researchers. Our work particularly focuses on the use of viewpoints in Open Distributed Processing (ODP) which is an ISO/ITU standardisation framework. The requirements of viewpoints modelling in ODP are very broad and, hence, demanding. Multiple viewpoints, though, prompt the issue of consistency between viewpoints. This paper describes a very general interpretation of consistency which we argue is broad enough to meet the requirements of consistency in ODP. We present a formal framework for this general interpretation; highlight basic properties of the interpretation and locate restricted classes of consistency. Strategies for checking consistency are also investigated. Throughout we illustrate our theory using the formal description technique LOTOS. Thus, the paper also characterises the nature of and options for consistency checking in LOTOS.