Modal specification theories for component-based design

Component-based software engineering has emerged as an important software engineering discipline to cope with the growing complexity of today’s software systems. Components are encapsulated software units with well-defined interfaces. A key principle of component-based development is to build larger systems by composition of smaller, less complex components. An important application area concerns reactive systems in which the modelling and verification of component behaviours is essential. To support correct usage and implementation of reactive components, interfaces should be equipped with rigorous formal specifications of component behaviours. This thesis presents a comprehensive study and analysis of specifications of interfaces for reactive components on the basis of modal input/output automata (MIOs), with a focus on interface refinement, interface composition and interface compatibility. MIOs are based on modal transition systems that were introduced by Larsen and Thomsen and that generalize labelled transition systems by distinguishing between may and must modalities for transitions. MIOs explicitly support loose specifications and offer an elegant approach to stepwise refinement. However, they lack a compatibility notion that is preserved by weak modal refinement, and support neither the integration of data specifications nor the specification of quantitative properties. In this thesis we develop an upwards and downwards closed hierarchy of novel specification theories for MIOs that remedy these shortcomings. Specification theories within the hierarchy are related by theory embeddings. The top element of our hierarchy of specification theories is given by a weak modal specification theory for MIOs including data and quantitative specifications, the bottom element is given by a strong modal specification theory for deterministic MIOs. On the one hand, we define MIOs with data constraints that integrate control flow and data flow of an interface. This new model extends MIOs by variables which are controlled by the owning component and visible to the environment. Transitions are augmented with preand postconditions to describe the dependencies between communication and data states. On the other hand, K -weighted MIOs address quantitative properties by labelling transitions with weights from a partially ordered weight structure K . This generalized formalism is capable of expressing constraints on non-functional properties such as