Counting Instances of Software Components

Component software is software that has been assembled from variouspieces of standardized, reusable computer programs, so-called components.Executing component software creates instances of these components. Forseveral reasons, for example, limited resources and/or application require-ments, it can be important to have control over the number of such instances.Clearly, design-time or compile-time control is to be preferred to run-time con-trol in cases where this is possible. We give an abstract component languageand a type system which ensures that the number of simultaneously activeinstances of any component never exceeds a (sharp) bound expressed in thetype. The language features instantiation and reuse of components, as wellas sequential composition, choice and scope. Alternatively one can view theobjects in the language as processes where the atomic actions are interpretedas either creating new, or reusing old instances.