Steps Towards a Method for the Formal Modeling of Dynamic Objects

Fragments of a method to formally specify object-oriented models of a universe of discourse are presented. The task of finding such models is divided into three subtasks, object classification, event specification, and the specification of the life cycle of an object. Each of these subtasks is further subdivided, and for each of the subtasks heuristics are given that can aid the analyst in deciding how to represent a particular aspect of the real world. The main sources of inspiration are Jackson System Development, algebraic specification of data- and object types, and algebraic specification of processes

A Rational Scheme for Conflict Detection and Resolution in Distributed Collaborative Environments for Enterprise Integration

A typical enterprise may have large numbers of information sources such as data stores, expert systems, knowledge-based systems, or standard software systems. These may need to be integrated so that, for example, an application program or a decision maker can access information from all these sources. Such architectures are generally called 'Distributed Collaborative Environments for Enterprise Integration'. A general problem in these enterprise integration architectures is that information from heterogeneous, pre-existing sources may be obsolete, incomplete, incorrect or, for many other reasons, contradictory. Thus, conflicting results may occur when the same information is requested from semantically related sources. A mechanism is required to detect and resolve these conflicts in a way that is rational to any potential client of the integration environment. This thesis lays open the design of a general mechanism for conflict detection and resolution that enables intelligent information agents to reason about contradictory information from pre-existing, heterogeneous and autonomous sources. The mechanism's theoretical basis is a framework that is drawn from evidence law, which shares some fundamental commonalities with conflict detection and resolution in enterprise integration environments. Conflict detection opens with gathering the results collected by the information retrieval process. These results may have justifications or certainty assessments attached to them. Furthermore, it identifies whether and how these results are conflicting. The design of a conflict resolution mechanism is based on a rational scheme for judging the weight of conflicting results. First, the agents assess the reliability or credibility of an information source. Judgement based on the weight of conflicting results is first applied to any available, domain-specific, resolution strategies. Second, the agent applies any 'general scientific' resolution strategies that are not specific to one domain. When no domain-related expertise can solve the conflict then the agent can only judge on domain independent evaluation criteria such as the results' reliability. A scheme is sketched out for judgement based on the reliability of conflicting results, involving three steps: Ranking the conflicting results according to their reliability; Ways to redefine conflicting results; and Heuristic decision-making. The evaluation includes a computational implementation of an enterprise integration environment incorporating a model of an information agent. An example is realised in this environment. The conflict detection and resolution mechanism, and interfaces to each integrated source, are implemented in Visual C++. A case study is conducted on this scenario to evaluate each conflict detection and resolution step. Furthermore, this illustrates both the advantages over existing approaches and the limitations

Studies related to the process of program development

The submitted work consists of a collection of publications arising from research carried out at Rhodes University (1970-1980) and at Heriot-Watt University (1980-1992). The theme of this research is the process of program development, i.e. the process of creating a computer program to solve some particular problem. The papers presented cover a number of different topics which relate to this process, viz. (a) Programming methodology programming. (b) Properties of programming languages. aspects of structured. (c) Formal specification of programming languages. (d) Compiler techniques. (e) Declarative programming languages. (f) Program development aids. (g) Automatic program generation. (h) Databases. (i) Algorithms and applications