A Grey-Box Approach to Component Composition

Abstract

Despite the obvious advantages of reuse implied by component technology, component based development has not taken off yet. Problems that inhibit general reuse include incomplete component contracts and (undocumented) dependencies of a component on the environment, which makes it hard to assess whether a component will behave in a particular setting as expected. In principle, a black-box approach to component deployment should be favored. In practice, however, we require information that cannot be described solely in terms of externally visible properties of components. For instance, non-functional properties (e.g., space and time requirements), environmental dependencies, and variation points (e.g., places where a component may be adapted or extended) do require insight in the internal construction of a component. In this paper, a grey-box approach to component deployment is discussed. It is based on a scenario-based technique called Use-Case-Maps (UCM), which uses scenarios to describe how several components operate at a high abstraction level. UCM is an informal notation. Its strong point is to show how things work generally. In order to reason about component compositions, we have augmented UCMs with formal specifications of component interfaces. These interface specifications have been borrowed from the concurrent, object-oriented language BCOOPL (Basic Concurrent Object-Oriented Programming Language). A BCOOPL interface is more than just a set of operations, it also describes temporal orderings of operations and the parties that are allowed to invoke a particular operation. The combination of UCMs and BCOOPL interfaces gives us the opportunity to document intra and inter component behavior at a high, but formal abstraction level.