Workflow Design Patterns

• Workflows are used in software applications to automate business processes.

• A workflow defines the sequence of steps or tasks that a business process should execute.

• The control flow workflow patterns describe the standard ways of task execution in a business process.

• Patterns used in use case to describe the behaviour

links

• http://www.workflowpatterns.com/patterns/control/

• https://www.sciencedirect.com/topics/computer-science/workflow-pattern

• https://docs.aws.amazon.com/amazonswf/latest/awsrbflowguide/programming-workflow-patterns.html

• https://en.wikipedia.org/wiki/Workflow_pattern

Libraries

• https://github.com/j-easy/easy-flows

• https://github.com/copper-engine/copper-engine

Types

workflows-examples.jpg

• (a) Sequential

  • Several tasks follow after one another

  • Task A needs to be done first, then Task B then Task C

  • Blocking tasks.

    • Task C needs to wait for Task B and Task A to be finished before starting

• (b) And split

  • After Task A is done, several tasks can begin at the same time

  • These tasks may not finish at the same time

  • These can be done in parallel and on seperate threads or processes

• (c) Synchronization

  • several concurrent activities to terminate before an activity can start

  • Normally associated with (b)

  • Must wait for all tasks to finish

• (d) XOR split

  • requires a decision

  • after the completion of task A, either B or C can be activated

  • Some sort of if/else or case/switch or strategy pattern

• (e) XOR join

  • several alternatives are merged into one

  • in our example task C is enabled when either A or B terminates

  • Race condition determines flow

• (f) OR split

  • is a construct to choose multiple alternatives out of a set.

  • after completion of task A, one could activate either B or C, or both

• (g) multiple merge

  • allows multiple activations of a task and does not require synchronization after the execution of concurrent tasks.

  • Once A terminates, tasks B and C execute concurrently

  • When the first of them, say B, terminates, then task D is activated; then, when C terminates, D is activated again.

• (h) discriminator

  • waits for a number of incoming branches to complete before activating the subsequent activity

  • then it waits for the outgoing branches to finish without taking any action until all of them have terminated. Next, it resets itself.

• (i) N out of M join

  • provides a barrier synchronization

  • Assuming that M > N tasks run concurrently, N of them have to reach the barrier before the next task is enabled

  • any two out of the three tasks A, B, and C have to finish before E is enabled

• (j) deferred choice

  • the choice is not made explicitly and the run-time environment decides what branch to take,