Workflow Design Patterns
Last updated
Last updated
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
(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,
