update and improve the process definition interchange language. In 2004 the WfMC endorsed BPMN, a graphical formalism to standardize the way that process definitions were visualized. XPDL was extended specifically with the goal of representing in XML all the concepts present in a BPMN diagram. This third revision of a process definition expression language is known as XPDL 2.0 and was ratified by the WfMC in October 2005. In April 2008, the WfMC ratified XPDL 2.1 as the fourth revision of this specification. XPDL 2.1 includes extension to handle new BPMN 1.1 constructs, as well as clarification of conformance criteria for implementations. In spring 2012, the WfMC completed XPDL 2.2 as the fifth revision of this specification. XPDL 2.2 builds on version 2.1 by introducing support for the process modeling extensions added to BPMN 2.0. References Wil M.P. van der Aalst, "Business Process Management Demystified: A Tutorial on Models, Systems and Standards for Workflow Management", Springer Lecture Notes in Computer Science, Vol 3098/2004. Wil M.P. van der Aalst, "Patterns and XPDL: A Critical Evaluation of the XML Process Definition Language", Eindhoven University of Technology, PDF. Jiang Ping, Q. Mair, J. Newman, "Using UML to design distributed collaborative workflows: from UML to XPDL", Twelfth IEEE International Workshops on Enabling Technologies: Infrastructure for Collaborative Enterprises, 2003. WET ICE 2003. Proceedings, . W.M.P. van der Aalst, "Don't go with the flow: Web services composition standards exposed", IEEE Intelligent Systems, Jan/Feb 2003. Jürgen Jung, "Mapping Business Process Models to Workflow Schemata An Example Using Memo-ORGML And XPDL", Universität Koblenz-Landau, April 2004, PDF. Volker Gruhn, Ralf Laue, "Using Timed Model Checking for Verifying Workflows", José Cordeiro and Joaquim Filipe (Eds.): Proceedings of the 2nd Workshop on Computer Supported Activity Coordination, Miami, USA, 23.05.2005 - 24.05.2005, 75-88. INSTICC Press . Nicolas Guelfi, Amel Mammar, "A formal framework to generate XPDL specifications from UML activity diagrams", Proceedings of the 2006 ACM symposium on Applied computing, 2006. Peter Hrastnik, "Execution of business processes based on web services", International Journal of Electronic Business, Volume 2, Number 5 / 2004. Petr Matousek, "An ASM Specication of the XPDL Language Semantics", Symposium on the Effectiveness of Logic in Computer Science, March 2002, PS. F. Puente, A. Rivero, J.D. Sandoval, P. Hernández, and C.J. Molina, "Improved Workflow Management System based on XPDL", Editor(s): M. Boumedine, S. Ranka, Proceedings of the IASTED Conference on Knowledge Sharing and Collaborative Engineering, St. Thomas, US Virgin