Workflow pattern


A workflow pattern is a specialized form of design pattern as defined in the area of software engineering or business process engineering. Workflow patterns refer specifically to recurrent problems and proven solutions related to the development of workflow applications in particular, and more broadly, process-oriented applications.

Concept

Workflow patterns are concepts of economised development. Their usage should follow strategies of simplifying maintenance and reducing modelling work.
Workflow is performed in real time. The mechanisms of control must support the typical pace of work. Design patterns must delay execution of workflow.

Aggregation

Workflow patterns may usually be aggregated as chains and the conditions for starting and terminating must be explicitly defined.

Application

Workflow patterns can be applied in various context, hence the conditions for use must be explicitly defined and shown in order to prevent misinterpretation.

Van der Aalst classification http://www.workflowpatterns.com

A well-known collection of workflow patterns is that proposed by Wil van der Aalst et al. in their paper Workflow Patterns. with earlier versions published in 2000-02. This collection of patterns focuses on one specific aspect of process-oriented application development, namely the description of control flow dependencies between activities in a workflow/process. These patterns are divided into the following categories:

Basic Control Patterns

The above workflow patterns have been used to evaluate the functionality of commercial products supporting the development of process-oriented applications. They have also been used to evaluate a number of proposed standards, including BPEL, BPMN, UML Activity diagram, XPDL, etc. It has been noted that not all these patterns are relevant in all application domains, so care must be taken when using the above workflow patterns to select a particular language or system for a given application.
The workflow patterns have also been used as initial requirements in the design of a workflow language and open-source system called YAWL.
Several extensions to the above set of workflow patterns have been proposed. In particular, the same research groups that developed these patterns, have also proposed a set of Workflow Data Patterns, Workflow Resource Patterns, Workflow Exception Handling Patterns, and Service Interaction Patterns.

Another classification

Another classification of workflow patterns is the following:
;Independent/Pooled: where each component of scheduled work is completed independent of each other component and no component has a specific dependency on any other component. An example would be where staff are serving at a counter - Raoul can serve a customer in his queue without waiting for Jamie to serve a customer in his queue.
;Sequential: where each component of scheduled work is dependent on the preceding component. In this case the preceding component controls the advancement of the workflow through subsequent components. An example would be on a production line - Betty cannot affix the radiator cap to the Model T Ford until Veronica has put the radiator in place.
;Interdependent/Networked: where each component of scheduled work is dependent on one or a number of other components being completed. In this case the preceding components control the workflow through subsequent components. An example would be a project team - Sarah must wait for several tasks to be completed by Kevin and George before she can execute her task.

Other perspectives

The workflow patterns are not limited to control-flow.
Other pattern collections include:
These patterns collections have been used to evaluate a variety of workflow processes, both commercial and open source.

Workflow systems implementing patterns

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