A Type System for Usage of Software Components

The aim of this article is to support component-based software engineering by modelling exclusive and inclusive usage of software components. Truong and Bezem describe in several papers abstract languages for component software with the aim to find bounds of the number of instances of components. Their language includes primitives for instantiating and deleting instances of components and operators for sequential, alternative and parallel composition and a scope mechanism. The language is here supplemented with the primitives use, lock and free. The main contribution is a type system which guarantees the safety of usage, in the following way: When a well-typed program executes a subexpression use[x] or lock[x], it is guaranteed that an instance of x is available