Overview

[December 27, 2002] Exchangeable Routing Language (XRL) is "an instance-based workflow language that uses XML for the representation of process definitions and Petri nets for its semantics. Since XRL is instance-based, workflow definitions can be changed on the fly and sent across organizational boundaries. These features are vital for today's dynamic and networked economy... The semantics of XRL are expressed in terms of Petri nets. Such formal semantics allow for powerful analysis techniques, an efficient and compact implementation, interfaces to many existing tools, and, last but not least, an unambiguous understanding of XRL. [The project team has developed a workflow management system, named XRL/flower, to support XRL. XRL/flower benefits from the fact that it is based on both XML and Petri nets. Standard XML tools can be deployed to parse, check, and handle XRL documents. The Petri net representation allows for a straightforward and succinct implementation of the workflow engine. XRL constructs are automatically translated into Petri net constructs. On the one hand, this allows for an efficient implementation. On the other hand, the system is easy to extend: For supporting a new routing primitive, only the translation to the Petri net engine needs to be added and the engine itself does not need to change. Last, but not least, the Petri net representation can be analyzed using state-of-the-art analysis techniques and tools." (adapted from the project home page)

[September 23, 2000] XRL is presented in a paper by W.M.P. van der Aalst and A. Kumar (College of Business and Administration, University of Colorado; Faculty of Technology and Management, Eindhoven University of Technology, The Netherlands). See below. The paper concludes: "The semantics of XRL was expressed in terms Petri nets by providing a direct mapping from each routing element to a Petri net construction. Thus, any workflow can be expressed in XRL and then translated into a Petri net representation, which lends itself easily to analysis. A full DTD for the schema has also been given to enable users to build their routing slips or schemas according to it and validate it using a standard XML tool. We are currently building a prototype that would implement this approach according to the architecture described in Section 3. This prototype benefits from the fact that it is based on both XML and Petri nets. Standard XML tools can be deployed to parse, check, and handle XRL documents. The Petri net representation allows for a straightforward and succinct implementation of the workflow engine. XRL constructs are automatically translated into Petri net constructs. One the one hand, this allows for an efficient implementation. On the other hand, the system is easy to extend: For supporting a new routing primitive, only the translation to the Petri net engine needs to be added and the engine itself does not need to change. Last-but-not-least, the Petri net representation can be analyzed using state-of-the-art analysis techniques and tools."

Principal References

• XRL website
• XRL XML DTD. 2002-12.
• "XRL Semantics." By Eric Verbeek. March 27, 2001. 10 pages. Diagrams providing detailed semantics for each constructs in terms of WF-nets. [cache]
• XRL XML DTD. 2002-06. Extracted from the ICATPN 2000 paper
• Project team:
  • W.M.P. van der Aalst (Faculty of Technology and Management, Eindhoven University of Technology, PO Box 513, NL-5600 MB, Eindhoven, The Netherlands). Email: w.m.p.v.d.aalst@tm.tue.nl
  • A. Kumar (Database Systems Research Department, Bell Laboratories 600 Mountain Ave., 2A-406, Murray Hill, NJ 07974, USA). Email: akhil@acm.org
  • H.M.W. Verbeek (Faculty of Technology and Management, Eindhoven University of Technology, PO Box 513, NL-5600 MB, Eindhoven, The Netherlands). Email: h.m.w.verbeek@tm.tue.nl
• Contact: W.M.P. van der Aalst

Articles, Papers, News

• [December 27, 2002] "XML Based Schema Definition for Support of Inter-organizational Workflow." By W.M.P. van der Aalst (College of Business and Administration, University of Colorado; Faculty of Technology and Management, Eindhoven University of Technology) and Akhil Kumar (Database Systems Research Department, Bell Laboratories). October 18, 2002. 39 pages. General Introduction to XRL, with 53 references on workflow. "The full potential of the web as a medium for electronic commerce can be realized only when multiple partners in a supply chain can route information among themselves in a seamless way. Commerce on the Internet is still far from being "friction-free" because business partners cannot exchange information about their business processes in an automated manner. In this paper, we propose the design for an eXchangeable Routing Language (XRL) using XML syntax. XML (Extensible Markup Language) is a means for trading partners to exchange business data electronically. The novel contribution of our work is to show how XML can also be used to describe workflow process schemas to support flexible routing of documents in the Internet environment. The design of XRL is grounded in Petri nets, which is a wellknown formalism. By using this formalism, it is possible to analyze correctness and performance of workflows described in XRL. Architectures to facilitate inter-operation through loose and tight integration are also discussed. Examples illustrate how this approach can be used for implementing interorganizational electronic commerce applications. As a proof of concept we have also developed XRL/flower, a prototype implementation of a workflow management system based on XRL..."

• [May 27, 2002] "XRL/Flower: Supporting Inter-Organizational Workflows Using XML/Petri-net Technology." By H.M.W. Verbeek, A. Hirnschall, and W.M.P. van der Aalst (Faculty of Technology Management, Eindhoven University of Technology, The Netherlands). Paper presented at Workshop on "Web Services, e-Business, and the Semantic Web (WES): Foundations, Models, Architecture, Engineering and Applications", held in conjunction with CAiSE 2002 [The Fourteenth International Conference on Advanced Information Systems Engineering , May 27-28, 2002, Toronto, Ontario, Canada]. Workshop proceedings pages 535-552. "In this paper, we present the architecture of XRL/Flower. XRL/Flower is a software tool which benefits from the fact that it is based on both XML and Petri nets. Standard XML tools can be deployed to parse, check, and handle XRL documents. The Petri-net representation allows for a straightforward and succinct implementation of the workflow engine. XRL constructs are automatically translated into Petri-net constructs. On the one hand, this allows for an efficient implementation. On the other hand, the system is easy to extend: For supporting a new routing primitive, only the translation to the Petrinet engine needs to be added and the engine itself does not need to change. Last, but not least, the Petri net representation can be analyzed using state-of-the-art analysis techniques and tools." [alt source]

• [July 14, 2001] "Verification of XRL: An XML-based Workflow Language." By W.M.P. van der Aalst, H.M.W. Verbeek, and A. Kumar. Paper presented at the The Sixth International Conference on CSCWD [Computer Supported Cooperative Work in Design] (July 12-14, 2001, London, Ontario, Canada); see abstracts and proceedings. "XRL (eXchangeable Routing Language) is an instance-based workflow language that uses XML for the representation of process definitions and Petri nets for its semantics. Since XRL is instance-based, workflow definitions can be changed on the fly and sent across organizational boundaries. These features are vital for today's dynamic and networked economy. However, the features also enable subtle, but highly disruptive, cross-organizational errors. On-the-fly changes and one-of-akind processes are destined to result in errors. Moreover, errors of a cross-organizational nature are difficult to repair. In this paper, we show soundness properties of XRL constructs by using a novel, constructive approach. We also describe a software tool based on XML and Petri-net technologies for verifying XRL workflows... we describe an automatic translation from XRL to Woflan. This way any workflow management based on XRL can benefit from state-of-theart verification software. Woflan is designed as a WFMS-independent analysis tool. In principle it can interface with many workflow management systems. At present, Woflan can interface with the workflow products COSA (Thiel Logistic AG/Software Ley), METEOR (LSDIS), and Staffware (Staffware), and the BPR-tool Protos (Pallas Athena). Woflan can read Petri Net Markup Language (PNML) files. PNML is a Petri net file format based on XML. Therefore, it is obvious to use XSL to automatically translate an XRL route into a PNML representation that can be diagnosed using Woflan. This translation can be done in a rather straightforward way; the only difficulty is the generation of unique names for the transitions and places used in the various constructs..." [cache]

• [June 26, 2000] "XML Based Schema Definition for Support of Inter-organizational Workflow." By W.M.P. van der Aalst and A. Kumar. Paper presented at the "Meeting on XML/SGML based Interchange Formats for Petri Nets," 21st International Conference on Application and Theory of Petri Nets [ICATPN 2000]. Aarhus, Denmark, June 26-30, 2000. 41 pages (with 40 references). "Commerce on the Internet is still seriously hindered by the lack of a common language for collaborative commercial activities. Although XML (Extensible Markup Language) allows trading partners to exchange semantic information electronically, it does not provide support for document routing. In this paper, we propose the design for an eXchangeable routing language (XRL) using XML syntax. Since XML is becoming a major international standard, it is understood widely. The routing schema in XRL can be used to support flexible routing of documents in the Internet environment. The formal semantics of XRL are expressed in terms of Petri nets and examples are used to demonstrate how it can be used for implementing inter-organizational electronic commerce applications. . . A core feature of XRL is that it provides a mechanism to describe processes at an instance level, i.e., an XRL routing schema describes the partial ordering of tasks for one specific instance. Traditional workflow modeling languages describe processes at a class or type level. Workflow instances, often referred to as cases, typically have a state which is expressed in terms of the class model. From an efficiency point of view, it is beneficial to split state (i.e., instance level) and process model (i.e., class level): If there are many instances of the same class, then duplication of routing information is avoided. However, in the context of inter-organizational workflow such a split is undesirable. It is unrealistic to assume that the different organizations share a common process model. Moreover, it should be possible to migrate instances (or parts of instances) from one organization to another without prior agreement on the precise order in which tasks are executed. Since the XRL routing schema describes the partial ordering of tasks for one specific instance instead of a class: (1) the schema can be exchanged more easily, (2) the schema can be changed without causing any problems for other instances, and (3) the expressive power is increased (workflow modeling languages typically have problems handling a variable number of parallel or alternative branches)... A Document Type Definition (DTD) which describes all the constructs is given in Appendix 1 using standard XML notation. The DTD contains markup declarations for the class of XRL documents. The document element, also called the root, is the route element. Any XRL document should be well-formed, i.e., taken as a whole it should match the production labeled document in the XML version 1.0 standard. Moreover, any XRL document should also be valid, i.e., the document should satisfy the constraints expressed by the declarations in the DTD. In Section 4, we introduced the XRL (eXchangeable Routing Language). The syntax of this language was defined in terms of a DTD. XRL is used to describe the dynamics of inter-organizational workflows. Therefore, it is of the utmost importance to have clear semantics for each of the constructs supported by XRL. For this purpose, we map XRL onto Petri nets. On the one hand, Petri nets can be used to represent the business logic in a graphical manner. In fact, the Petri net language is close to many of the diagramming languages used by both commercial workflow management systems and researchers active in this domain. For example, workflow management systems and ERP systems such as COSA (Software Ley), Income (Promatis), BaanERP (Baan), and ARIS/SAP (IDL/SAP) use (variants of) Petri nets. On the other hand, Petri nets are a formal language with clear semantics, powerful analysis techniques, and strong theoretical results. By mapping XRL onto Petri nets, we give formal semantics, are able to reason about XRL (e.g., about its expressive power), can use state-of-the-art analysis techniques, and can use existing software..." [cache]

• On XML and Petri Nets, see "Petri Net Markup Language (PNML)."

• On XML and workflow, see

  • "Business Process Execution Language for Web Services (BPEL4WS)
  • XML-Based Workflow [Process Management] Standard: Wf-XML
  • XML for Workflow Management [NIST]
  • SWAP - Simple Workflow Access Protocol