1 A Formal Model for

We present a formal model for component systems which provides precise mathematical deenitions for concepts like component, interface, type and instance, as well as dynamic behavior and changes of system structure over time. Based on these concepts, we deene the semantics of intuitive, commonly used graphical description techniques as an interpretation in terms of the presented system model. Several exemplary description techniques illustrate the feasibility of our approach. The essence of componentware is to build well-structured systems out of independently understandable and reusable building blocks. However, with the rise of pragmatic technologies like ActiveX Mic98], JavaBeans Jav99b], and Enterprise JavaBeans Jav99a] as well as the growing interest in reuse and reengineering of legacy components it is evident that a solid, uniied understanding and scientiic models of componentware are still missing. Even central concepts like \component" or \interface" are deened and used in very diierent ways by diierent authors. Although existing Architecture Deenition Languages, like Rapide LKA + 95], UniCon SDK + 95], or Wright AG97] introduce these concepts on a more formal basis, they do not adequately consider all relevant behavior-related aspects of a component system and are sometimes diicult to apply in practice NR99]. We believe that a clearly deened conceptual model designed for componentware development is essential, especially as a foundation for an overall componentware methodology comprising the integration of suitable graphical description techniques, tool support, and development process models BRSV98]. Only then it is possible to answer typical questions like \What does this particular component do?", \Will these interfaces match?", and \Are these diierent system descriptions equivalent?" which are commonly posed during system development. A fruitful discussion about such issues requires a precisely deened language as well as a comprehensive theory to reason about the behavior of a component sys