Dependable compositions: a formal approach

Abstract

Design processes for most engineering disciplines are based on component reuse. In much the same way as the need for customizable reuse of software fueled the growth and development of object-oriented programming languages over module-based languages, the same driving force for component-based solutions is leading to object-oriented languages being transcended by component-based composition languages. Existing declarative programming languages are ideally suited to the construction of software components, but are inappropriate for specifying compositions of components in a high level manner. Indeed several composition environments exist that are built on top of object-oriented languages though they fail to supply the level of abstraction required to specify compositions of components. This is particularly true when the components are black boxes. In order to reuse a black box component, an accurate and unambiguous description of the component's functionality must exist. It is doubtful that natural language can fulfil this requirement. This thesis advocates a formal approach to specifying a component and demonstrates that this approach will aid in the composition and verification of component based systems. The thesis presents a general solution to the problem by defining the formal semantics for a composition of components. Building on this work, a formal definition of exceptional component behaviour is provided along with a formal reasoning about component dependability. These then form the basis for the formal definition of a composition specification language and theoretical declarative compositional programming language. Such a language would afford the programmer the tools required to construct a dynamic composition of components.