1. Andrews, T., Curbera, F., Dholakia, H., Goland, Y., Klein, J., Leymann, F., Liu, K., Roller, D., Smith, D., Thatte, S., Trickovicand, I., Weerawarana, S.: Business process execution language for web services v-1.1, W3C. Candidate recommendation (2003)
2. WfMC, Workflow management coalition workflow standard: Workflow process definition interface - XML process definition language (XPDL) (wfmc-tc-1025). Workflow Management Coalition, Lighthouse Point, (FL), Tech. rep. (2002)
3. Erol, K., Hendler, J., Nau, D.S.: Semantics for hierarchical task-network planning, University of Maryland, College Park, MD, USA, Tech. Rep. (1994)
4. Sycara, K., Williamson, M., Decker, K.: Unified information and control flow in hierarchical task networks. In: Working Notes of the AAAI 1996 workshop, Theories of Action, Planning, and Control (1996)
5. Sadiq, W., Orlowska, M.E.: Modeling and verification of workflow graphs. Technical Report No. 386, Department of Computer Science. The University of Queensland, Australia (1996)