Work ow Management Systems (WfMSs) enable the development and maintenance of work ow speci cations at design time and their execution and monitoring at runtime. The open source WfMS YAWL supports the YAWL language { a formally de ned language based on Petri nets which o ers comprehensive support for control- ow and resource patterns. In addition, the YAWL system provides extensive support for process exibility, in particular for process con guration, exception handling, dynamic work ow and declarative work ow. Due to its formal foundation, sophisticated veri cation support can also be achieved. This paper presents the YAWL system and its main applications.
with a collection of resource patterns and comprehensive support for these patterns in the YAWL environment was recently realised. 2
Some of the fundamental goals of the YAWL environment include that it should be freely available, portable, easy to use and interoperable. By releasing the environment under an open source license free availability was achieved. Portability was achieved through the use of JavaTM and by avoiding any operating system dependencies. Ease of use was realised by the provision of an intuitive user interface for creating and executing speci cations. Finally, interoperability was supported by a service-oriented architecture, the de nition of a common XML format and a set of API calls for the exchange of work ow speci cations between design time and runtime environment.
` Process Designer
Process Repository
YAWL Engine
Interfaces
Resource Service Admin Users Applications
Persisted Data Event Logs Org Data Event Logs
Other Custom Services
The three main components of the YAWL system are the Editor, the Engine and the Resource Service, which communicate through well-de ned interfaces (see Figure 1). They all are connected through the underlying service-oriented architecture. Based on this architecture users can adapt the YAWL system to their needs and introduce their own custom services where required.
The Editor provides a tool palette from which modeling elements (such as tasks or conditions) may be chosen for placement on the design canvas (see Figure 2). Routing constructs may be attached to tasks, and arcs added to link tasks and conditions, in order to form a complete work ow graph capturing a particular business process. At any time a work ow model may be veri ed using various algorithms to ensure completeness and soundness, amongst other things. The Editor communicates with a running Engine to receive a list of YAWL Services which are registered with the Engine. A work ow designer can then associate those services with tasks of a work ow speci cation. Furthermore, from a running Resource Service, the Editor obtains organizational resources and socalled codelets. Within the Editor tasks can be associated with those resources, which are o ered the according workitem at runtime. Furthermore, a work ow designer can automate a task by assigning a codelet, which is a small Java based application executed for the task at runtime.
The Engine deals with control- ow logic and data passing, but is resourceagnostic. Valid work ow speci cations are loaded into the Engine and stored in a repository from where they may be instantiated to produce cases. The Engine is in charge of the execution of cases and determines which workitems are enabled throughout the process lifecycle. Work ow data can be updated through the execution of workitems and be passed between work ow elements or e.g. be used for the evaluation of routing conditions.
The Resource Service ensures the correct routing of workitems to resources. It consists of the following four sub-services: A Resource Manager, which manages the allocation of resources to workitems; a Worklist Handler { a web-form based user interface that provides users with the ability to interact with and to process workitems; a Forms Connector to visualize tailor-made and/or dynamically generated web-forms for displaying and editing workitem data; and a Codelet Service that maintains and executes codelets selected for automated tasks.
The YAWL system has been downloaded from SourceForge more than 80,000 times4. Being open source, and thus freely available, and having a solid theoretical base, makes the YAWL environment suitable for tertiary education | at least 24 universities worldwide have used it in their teaching. The original YAWL paper5 has attracted over 400 citations according to Google Scholar and is the second most cited paper to appear in Information Systems according to Scopus.
The Australian Film, Television & Radio School (AFTRS) and the Queensland University of Technology (QUT) started the YAWL4Film ini- Fig. 3. A dynamically generated form. tiative in 2007 in the context of the ARC Centre of Excellence for Creative Industries and Innovation. As part of this collaboration a solution was developed for lm shoot production data management and report generation which uses YAWL. This solution was trialed in two student projects at the AFTRS and it was further adapted for the shooting of the commercial feature lm \Prime Mover" in the Australian outback.6 rst:utility and rst:telecom in the UK, both part of the Impello plc group of companies, providing energy and telecoms services respectively, have been collaborating with QUT since 2005 on the YAWL initiative. These companies have built software around the YAWL system providing a novel approach to page navigation for web based systems together with the more traditional use of choreographing long-lived business processes.7 4
Future work for the YAWL system is anticipated to include sophisticated workow monitoring, conceptual process integration primitives, improved support for forms generation and templating, and system integration. 4 https://sourceforge.net/projects/yawl 5 W.M.P. van der Aalst and A.H.M. ter Hofstede. YAWL: Yet Another Work ow
Language. Information Systems, 30(4):245{275, 2005 6 http://www.primemovermovie.com 7 Quoted almost verbatim from http://www.yawlfoundation.org/about/adoption.html.