Semantics and Verification of UML Activity Diagrams for Workflow Modelling

This thesis defines a formal semantics for UML activity diagrams that is suitable for workflow modelling. The semantics allows verification of functional requirements using model checking. Since a workflow specification prescribes how a workflow system behaves, the semantics is defined and motivated in terms of workflow systems. As workflow systems are reactive and coordinate activities, the defined semantics reflects these aspects. In fact, two formal semantics are defined, which are completely different. Both semantics are defined directly in terms of activity diagrams and not by a mapping of activity diagrams to some existing formal notation. The requirements-level semantics, based on the Statemate semantics of statecharts, assumes that workflow systems are infinitely fast w.r.t. their environment and react immediately to input events (this assumption is called the perfect synchrony hypothesis). The implementation-level semantics, based on the UML semantics of statecharts, does not make this assumption. Due to the perfect synchrony hypothesis, the requirements-level semantics is unrealistic, but easy to use for verification. On the other hand, the implementation-level semantics is realistic, but difficult to use for verification. A class of activity diagrams and a class of functional requirements is identified for which the outcome of the verification does not depend upon the particular semantics being used, i.e., both semantics give the same result. For such activity diagrams and such functional requirements, the requirements-level semantics is as realistic as the implementation-level semantics, even though the requirements-level semantics makes the perfect synchrony hypothesis. The requirements-level semantics has been implemented in a verification tool. The tool interfaces with a model checker by translating an activity diagram into an input for a model checker according to the requirements-level semantics. The model checker checks the desired functional requirement against the input model. If the model checker returns a counterexample, the tool translates this counterexample back into the activity diagram by highlighting a path corresponding to the counterexample. The tool supports verification of workflow models that have event-driven behaviour, data, real time, and loops. Only model checkers supporting strong fairness model checking turn out to be useful. The feasibility of the approach is demonstrated by using the tool to verify some real-life workflow models

Assessing suitability of adaptive case management

Business Process Management (BPM) includes methods and techniques to support the execution of business processes. In recent years, Adaptive Case Management (ACM) has been proposed as new BPM technology for supporting knowledge-intensive processes. However, there is currently no structured way of quickly deciding upon the suitability of an ACM system to a specific business process. This paper presents a framework for assessing to which extent ACM is suitable for a particular business process. It distinguishes between process characteristics that ACM can support, characteristics that ACM can support but are not ideal, and characteristics that ACM cannot support. The framework also explains the rationale behind each assessment, and refers to alternatives in case ACM is not suitable for the process that needs to be supported. Thus, the framework provides a transparent and useful advice about which kind of BPM technology is most suitable to support a business process to the best extent. A preliminary evaluation of the framework has been carried out in collaboration with an IT consultancy company that advises its clients on BPM technology

Comparing Refinements for Failure and Bisimulation Semantics

Refinement in bisimulation semantics is defined differently from refinement in failure semantics: in bisimulation semantics refinement is based on simulations between labelled transition systems, whereas in failure semantics refinement is based on inclusions between decorated traces systems. There exist however pairs of refinements, for bisimulation and failure semantics respectively, that have almost the same properties. Furthermore, each refinement in bisimulation semantics implies its counterpart in failure semantics, and conversely each refinement in failure semantics implies its counterpart in bisimulation semantics defined on the canonical form of the compared processes

An integer programming based approach for diagnosing workflows

Workflow analysis is indispensable to capture modeling errors in workflow designs. While in the past several analysis approaches for workflows have been defined, these approaches do not give precise feedback, making it hard for a designer to pinpoint the exact cause of modeling errors. In this paper we introduce a novel approach for analyzing and diagnosing workflows based on integer programming (IP). Each workflow model is translated into a set of IP constraints. Faulty control flow connectors can be easily detected using the approach by relaxing the corresponding constraints. We show that this approach is correct, and illustrate it with realistic examples where the CPLEX tool is used to solve the IP formulations. Moreover, the approach is flexible and can be extended to handle a variety of new constraints, as well as to support new workflow patterns. Its features complement those of existing approaches