Comparison of ODP Viewpoint Specifications: A Case Study

The viewpoint approach to specification, in which a system is described by several partial specifications, each dealing with a different aspect or perspective, has been proposed as a way of making complex distributed computing systems more manageable and understandable. The ISO's Open Distributing Processing (ODP) framework is a particular variant of the viewpoint approach, being developed into an international standard for the specification of open distributed systems. It involves five specifically named viewpoints, including the Information Viewpoint (a high-level specification of the information processed by the system) and the Enterprise Viewpoint (which focusses on the overall scope, purpose, and policies of the system). This report uses a case study of a lending library to compare two partial specifications of a system --- one representing the Information Viewpoint, and the other the Enterprise Viewpoint --- and attempts to draw some conclusions regarding the relation between the two viewpoints. Both specifications are written in Object-Z, an object-oriented specification language developed from standard Z. Examining how two such partial specifications might be unified into a single specification raises many general issues regarding the mutual consistency of partial specifications, and regarding the nature of specification refinement in Object-Z. The report identifies some of the problems involved, and suggests areas worthy of further, more formal, investigation.