TTMS: A Task Tree Based Workflow Management System

In this paper, an approach to use task trees in a workflow management system (WfMS) is presented. As hierarchical models task trees capture several hierarchy levels of a workflow in one model. A workflow editor visualizes the models also as flowcharts similar to UML activity diagrams. The WfMS use these models as input and instantiates and executes them. The system is web-based and can be easily accessed by users with any browser clients. This paper motivates the approach to use task trees that produce hierarchical and structured workflow specifications. The proposed language might help end-users to better understand workflow models with its problem oriented hierarchical modeling character. Temporal operators from the task models are compared with certain operators from established workflow languages. In addition, in TTMS an instantiation time concept is implemented, where decision operators are evaluated at the very moment the process is instantiated. Consequently the task tree modeling language is enhanced for modeling decisions in the context of workflow management.