To meet the data management requirements of new complex applications, object management systems are emerging as the most likely candidate. The general acceptance of this new technology depends on the increased functionality it can provide, and one measurement is the power of its query model. Users of these systems must have a declarative language to formulate queries on "what" information is required without specifying "how" to efficiently retrieve the information. Therefore, the formal query model should define a declarative calculus that can be used to formulate queries to the objectbase and an equivalent procedural algebra to execute them efficiently. In addition, a user-level language should be provided which has the same expressive power as the formal languages. This thesis presents the new TIGUKAT Language that was designed and implemented within the framework of the TIGUKAT project. It is a high level user language which provides declarative access to the underlying objectbase. ...

Both object-orientation and the Internet make the widespread reuse of software a possibility. Unfortunately, the potential benefits from these facilities have not been forthcoming. One reason for this is the lack of a coherent model for software development and reuse. This paper proposes such a model which is based upon modelling software components using state transition machines. Reuse is made possible by defining matching relations between component descriptions in terms of machine simulations. Both the development process and matching relations are given a formal semantics. 2 Introduction The reuse of software components has long been a major aim of Software Engineering [12]. We propose that there are two major reasons why this aim has not yet been realised. Firstly, no single organisation can afford to develop all the software which it will subsequently need to reuse (and until recently there has been no effective mechanism which allows different organisations to pool software r...