Frequently Asked Questions

FAQ - Is YAWL released under an open source copyright licence?

Both the YAWL workflow engine and the YAWL workflow editor are released under the LGPL licence.
Rather than repeating the common reasons for adopting open-source here, please use the following resources to familiarise yourselves with our reasons for adopting open source licensing:

FAQ – What is the relation between YAWL and Petri Nets

To a large extent YAWL was inspired by Petri-Nets, however a common misconception is that YAWL is simply a set of "macro like" extensions for Coloured Petri-Nets. YAWL extends Petri nets with concepts for multiple instances (where at runtime a task may have multiple instances active at the same time), the generalised OR-join (where a construct only waits for further triggers if these can indeed arrive) and cancellation (where a collection of activities can be terminated through the execution of a certain task). Details on these extensions can be found in the YAWL Paper.

FAQ – How does YAWL compare to BPMN, BPEL, UML and EPCs?

Firstly, YAWL provides stronger support for the workflow patterns (e.g. see here). Of particular note are YAWL’s support for the control-flow perspective and the resource perspective. Generally speaking the stronger patterns support means that it is easier to specify complex workflows.

Secondly, YAWL has a formal semantics. This means that it is not necessary to debate the precise meaning of certain constructs and that there shouldn’t be a discrepancy between a model and its implementation due to interpretation differences. As a result of having a formal semantics, YAWL can offer powerful means for design time workflow checks (see e.g. the paper business process verification - finally a reality!

Thirdly, YAWL offers comprehensive support for dynamic workflow, where workflows need to change after their deployment and for handling unexpected exceptions. In many realistic scenarios processes evolve and not all exceptions are foreseen. Through the Worklet service, dynamic flexibility and exception handling support change, even while a process instance is executing. Through the DECLARE service YAWL can offer support for workflows that are loosely structured and are best specified through constraints. All in all this means that YAWL offers superior flexibility support (see also this paper).

Compared to BPMN it is striking that YAWL can handle more control-flow patterns yet is considerably simpler in terms of the number of available contructs (and their meaning). Also, in contrast to BPMN, UML and EPCs, YAWL models are executable (and it should be noted that the mapping from BPMN to BPEL is far from straightforward, see e.g. From Business Process Models to Process-oriented Software Systems: the BPMN to BPEL Way).

Compared to BPEL, YAWL has a graphical front-end and as such its specifications should be easier to use in communication with stakeholders.

FAQ – Where can I find documentation on YAWL?

We have produced research papers about YAWL and we have written some papers about Control-flow Patterns , Data Patterns and Resource Patterns.

Also this website contains many resources: describing the elements of YAWL and some executable examples of YAWL process models.

FAQ - What aspects of BPM/Workflow are supported?

  • YAWL offers comprehensive support for the workflow patterns, in particular the control-flow patterns and the resource patterns. To our knowledge, no existing BPM environment, be it commercial or open source, is as comprehensive in its support for the workflow patterns.
  • YAWL offers unique support for flexibility. The worklet service can deal with workflows that need to evolve over time, while in the declare service loosely structured workflows can be specified.
  • YAWL offers unique support for exception handling. This approach is based on the exception handling patterns. New exceptions may emerge over time and the way these are to be handled can be seamlessly integrated.
  • The YAWL system is one of the most open BPM environments in existence. Its Service-Oriented Architecture offers many different interfaces that external programs, including other BPM environments, can link to.
  • The YAWL editor provides a graphical front end for workflow specification.
  • Through a link with the ProM environment powerful analytic support is available based on information captured in log files. Work on simulation support has also begun.
  • YAWL offers two approaches to verification (one based on the wofYAWL package and the other directly built into the editor). Thus powerful support exists for determining whether a workflow is sound at design time.
  • Timers can be specified for tasks. These may be specified to begin on enablement of a task or upon execution start of a task.
  • Automated support for screen generation is provided through JavaServer Faces Technology. You also have the choice to link custom made screens to tasks.
  • The YAWL environment can run (at least) with the following databases: PostgreSQL, MySQL, Apache Derby, ORACLE and HSQLDB.

FAQ – What are the benefits of using YAWL?

Without becoming repetitive, YAWL is a very powerful state-of-the art BPM environment, which is open source, and aims to be easy to use and to install. The latest academic insights are continuously integrated into the environment and hence it is uniquely positioned.