YAWL
Encyclopedia
This article is about the workflow system. For the sailing craft, see yawl
.
YAWL (Yet Another Workflow Language) is a workflow
language based on the Workflow patterns
. The language is supported by a software system that includes an execution engine, a graphical editor and a worklist handler. The system is available as Open source
software under the LGPL license.
Production-level uses of the YAWL system include a deployment by first:utility and first:telecom in the UK to automate front-end service processes, and by the Australian film television and radio school
to coordinate film shooting processes. The YAWL system has also been used for teaching in more than 20 universities.
and Queensland University of Technology
. Subsequently, several organizations such as InterContinental Hotels Group
, first:telecom and ATOS Worldline have contributed to the initiative.
The original drivers behind YAWL were to define a workflow language that would support all (or most) of the Workflow Patterns and that would have a formal semantics. Observing that Petri nets came close to supporting most of the Workflow Patterns, the designers of YAWL decided to take Petri nets as a starting point and to extend this formalism with three main constructs, namely or-join, cancellation sets, and multi-instance activities. These three concepts are aimed at supporting five of the Workflow Patterns that were not directly supported in Petri nets, namely synchronizing merge, discriminator, N-out-of-M join, multiple instance with no a priori runtime knowledge and cancel case. In addition, YAWL adds some syntactical elements to Petri nets in order to intuitively capture other workflow patterns such as simple choice (xor-split), simple merge (xor-join), and multiple choice (or-split). During the design of the language, it turned out that some of the extensions that were added to Petri nets were difficult or even impossible to re-encode back into plain Petri nets. As a result, the original formal semantics of YAWL is defined as a Labelled transition system and not in terms of Petri nets. The fact that YAWL is based on a formal semantics has enabled the implementation of several techniques for analyzing YAWL processes. In particular, the YAWL system includes a static analysis tool called WofYAWL.
. This has paved the way for the development of static analysis tools for BPEL that can compete with the static analysis capabilities provided by the YAWL system. On the other hand, it has been noted that standard BPEL fails to support human tasks, that is, tasks that are allocated to human actors and that require these actors to complete actions, possibly involving a physical performance. A number of BPEL engines already provide extensions to BPEL for human tasks, but these extensions are yet to be standardized. In contrast, YAWL provides a unified interface for worklist services based on Web services standards. This interface allows developers to build their own worklist service to support human tasks according to their needs. In addition, the YAWL system comes with a default worklist service that supports several types of human task allocation and handling. Another advantage of YAWL is its support for the Workflow Patterns, although the gap between YAWL and BPEL in this respect may be reduced by new constructs that are included in BPEL version 2.0.
Yawl
A yawl is a two-masted sailing craft similar to a sloop or cutter but with an additional mast located well aft of the main mast, often right on the transom, specifically aft of the rudder post. A yawl (from Dutch Jol) is a two-masted sailing craft similar to a sloop or cutter but with an...
.
YAWL (Yet Another Workflow Language) is a workflow
Workflow
A workflow consists of a sequence of connected steps. It is a depiction of a sequence of operations, declared as work of a person, a group of persons, an organization of staff, or one or more simple or complex mechanisms. Workflow may be seen as any abstraction of real work...
language based on the Workflow patterns
Workflow patterns
A workflow pattern is a specialized form of a design pattern as defined in the area of software engineering or business process engineering respectively...
. The language is supported by a software system that includes an execution engine, a graphical editor and a worklist handler. The system is available as Open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
software under the LGPL license.
Production-level uses of the YAWL system include a deployment by first:utility and first:telecom in the UK to automate front-end service processes, and by the Australian film television and radio school
Australian Film Television and Radio School
The Australian Film, Television and Radio School is the Australian national centre for professional education and advanced training in film, television, radio and digital media. The School is an Australian Commonwealth government statutory authority...
to coordinate film shooting processes. The YAWL system has also been used for teaching in more than 20 universities.
Features
- Comprehensive support for the workflow patterns.
- Support for advanced resource allocation policies, including four-eyes principleTwo-man ruleThe two-man rule is a control mechanism designed to achieve a high level of security for especially critical material or operations. Under this rule all access and actions requires the presence of two authorized people at all times.-Nuclear weapons:...
and chained execution. - Support for dynamic adaptation of workflow models through the notion of worklets.
- Sophisticated workflow model validation features (e.g. deadlock detection at design-time).
- XML-based model for data definition and manipulation based on XML SchemaXML SchemaXML Schema, published as a W3C recommendation in May 2001, is one of several XML schema languages. It was the first separate schema language for XML to achieve Recommendation status by the W3C...
, XPathXPathXPath is a language for selecting nodes from an XML document. In addition, XPath may be used to compute values from the content of an XML document...
and XQueryXQuery- Features :XQuery provides the means to extract and manipulate data from XML documents or any data source that can be viewed as XML, such as relational databases or office documents....
. - XML-based interfaces for monitoring and controlling workflow instances and for accessing execution logs.
- XML-based plug-in interfaces for connecting third-party web services with the system, including third-party worklist/task handlers.
- Automated form generation from XML schema.
History
The language and its supporting system were originally developed by researchers at Eindhoven University of TechnologyEindhoven University of Technology
The ' is a university of technology located in Eindhoven, Netherlands. The motto of the university is: Mens agitat molem . The university was the second of its kind in the Netherlands, only Delft University of Technology existed previously. Until mid-1980 it was known as the...
and Queensland University of Technology
Queensland University of Technology
Queensland University of Technology is an Australian university with an applied emphasis in courses and research. Based in Brisbane, it has 40,000 students, including 6,000 international students, over 4,000 staff members, and an annual budget of more than A$750 million.QUT is marketed as "A...
. Subsequently, several organizations such as InterContinental Hotels Group
InterContinental Hotels Group
InterContinental Hotels Group plc is a global hotels company headquartered in Denham, United Kingdom. It is the largest hotels company in the world measured by rooms , and has over 4,500 hotels across over 100 countries...
, first:telecom and ATOS Worldline have contributed to the initiative.
The original drivers behind YAWL were to define a workflow language that would support all (or most) of the Workflow Patterns and that would have a formal semantics. Observing that Petri nets came close to supporting most of the Workflow Patterns, the designers of YAWL decided to take Petri nets as a starting point and to extend this formalism with three main constructs, namely or-join, cancellation sets, and multi-instance activities. These three concepts are aimed at supporting five of the Workflow Patterns that were not directly supported in Petri nets, namely synchronizing merge, discriminator, N-out-of-M join, multiple instance with no a priori runtime knowledge and cancel case. In addition, YAWL adds some syntactical elements to Petri nets in order to intuitively capture other workflow patterns such as simple choice (xor-split), simple merge (xor-join), and multiple choice (or-split). During the design of the language, it turned out that some of the extensions that were added to Petri nets were difficult or even impossible to re-encode back into plain Petri nets. As a result, the original formal semantics of YAWL is defined as a Labelled transition system and not in terms of Petri nets. The fact that YAWL is based on a formal semantics has enabled the implementation of several techniques for analyzing YAWL processes. In particular, the YAWL system includes a static analysis tool called WofYAWL.
YAWL vs. BPEL
YAWL is sometimes seen as an alternative to BPEL. A major advantage of BPEL is that it is driven by a standardization committee supported by several IT industry players. As a result, BPEL is supported by a significant number of tools (both proprietary and open-source) while YAWL has a single implementation at present. Also, several researchers have captured the formal semantics of subsets of BPEL in terms of various formalisms, including Petri nets, Process algebra and Finite state machineFinite state machine
A finite-state machine or finite-state automaton , or simply a state machine, is a mathematical model used to design computer programs and digital logic circuits. It is conceived as an abstract machine that can be in one of a finite number of states...
. This has paved the way for the development of static analysis tools for BPEL that can compete with the static analysis capabilities provided by the YAWL system. On the other hand, it has been noted that standard BPEL fails to support human tasks, that is, tasks that are allocated to human actors and that require these actors to complete actions, possibly involving a physical performance. A number of BPEL engines already provide extensions to BPEL for human tasks, but these extensions are yet to be standardized. In contrast, YAWL provides a unified interface for worklist services based on Web services standards. This interface allows developers to build their own worklist service to support human tasks according to their needs. In addition, the YAWL system comes with a default worklist service that supports several types of human task allocation and handling. Another advantage of YAWL is its support for the Workflow Patterns, although the gap between YAWL and BPEL in this respect may be reduced by new constructs that are included in BPEL version 2.0.