Compositional design and verification of component-based information systems

Abstract

Information systems have to support more and more complex organizations and the cooperation between organizations. The functionality of these systems is divided in components: each component has its own dedicated set of functionality. Whereas in past years, design and verification mostly focused on the internal aspects of a component, like the data aspect and behavioral aspect, the focus nowadays shifts more and more to the design and verification of the interaction between systems. Different organizations provide systems that need to communicate. Specifically, an organization may allow its components to be used by systems of other organizations. This way, an inter organizational network of communicating components is formed. One of the main aspects of such a network is that organizations do not want to share with whom they are communicating. This way, the individual systems form a, possibly unknown, large scale ecosystem: a dynamic network of communicating components. These systems communicate via messages: a component requests a service from another component, which in turn eventually sends its answer. Hence, communication between the components is asynchronous by nature. Verification of asynchronously communicating systems is known to be a hard problem. In this thesis, we develop a framework to design large scale component-based information systems in which components communicate asynchronously. The framework allows for verification of local conditions for termination of the complete system. The formal foundation of the framework is Petri nets, in which communication is asynchronous by nature. Classical Petri nets can be used both for modeling the internal activities of a component, as well as for the interaction between components. We focus on soundness of systems: a system should always have a possibility to terminate. We propose sufficient criteria for compositional verification of soundness: if each component in the system is sound, and each pair of asynchronously communicating components satisfies some condition, the whole system is sound. The framework provides methods to design components that are sound by construction. The method uses soundness preserving refinements of Petri net places in different components by pairs of sound subcomponents. Data can be used to enrich the behavioral aspect, the control flow, of an information system, and data is used to store and present information to the users of the system. Classical Petri nets only focus on the ordering of activities. To integrate the data aspect and behavioral aspect of components, we define a sub class of coloured Petri nets, which is on the one hand expressive enough to model the flow and correlation of objects and messages, and on the other hand the possibility of verification remains. All techniques are combined in a design approach for the development of component based information systems. The approach uses the framework to develop a formal specification from user requirements. The developed specification is directly usable as a prototype, as it has execution semantics. The tool Yasper is developed to support the approach. Process mining techniques can be used to support the design process of component based information systems, by extracting internal aspects of a component, like data, resources and control flow. In the thesis, we present a process discovery algorithm based on integer linear programming, which can be used for this purpose, as it can handle negative instances that describe undesired behavior.