A Formalization of an Extended Object Model Using Views
Reuse of software designs, experience and components is essential to making substantial improvements in software productivity, development cost, and quality. However, the many facets of reuse are still rarely used in the various phases of the software development lifecycle because of a lack of adequate theories, processes, and tools to support consistent application of reuse concepts. There is a need for approaches including definitions, models and properties of reuse that would provide explicit guidance to a software development team in applying reuse. In particular there is a need to provide abstractions that clearly separate the various functional concerns addressed in a software system. Separating concerns simplifies the identification of the software components that can benefit from reuse and can provide guidance on how reuse may be applied. In this thesis we present an extended model related to the separation of concerns in object-oriented design. The model, called views, indicates how an object-oriented design can be clearly separated into objects and their corresponding interfaces. In this model objects can be designed so that they are independent of their environment, because adaptation to the environment is the responsibility of the interface or view. The view can be seen as expressing the semantics for the 'glue' that joins components or objects together to create a software system. Informal versions of the views model have already been successfully applied to operational and commercial software systems. The objective of this thesis is to provide the views notion with a theoretical foundation to address reuse and separation of concerns. After clearly defining the views model we show the formal approach to combining the objects, interfaces (views), and their interconnection into a complete software system. The objects and interfaces are defined using an object calculus based on temporal logic, while the interconnections among object and views are specified using category theory. This formal framework provides the mathematical foundation to support the verification of the properties of both the components and the composite software system. We then show how verification can be mechanized by converting the formal version of the views model into higher-order logic and using PVS to support mechanical proofs.