Defining a Workflow

When you define a workflow, your activity diagram should answer the following questions:

• Who or what has overall responsibility for the workflow?

  A use case or class could own each activity diagram, for example.

• What activities need to be performed to meet your objective or goal?

  Define all of the high-level activities that need to take place in the workflow. You do not need to define every activity or state, just the ones with the greatest importance in the workflow.

• Who will be responsible for performing the various activities and states?

  Define each activity within a swimlane so you know who is responsible for carrying out the activity. Any element within a swimlane is owned and should be carried out by the swimlane.

• Do the activities create or modify objects?

  Connect objects and activities with object flows. Specify the state of the object through the state specification.

• Where do the activities and states take place with respect to other elements on your diagram?

  Placement of your activities on the diagram determines the order of your workflow.

• Why does this activity or state need to take place?

  The reason or purpose for each activity or state should be placed in the specification Documentation field.

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Modeling a Workflow with an Activity Diagram

Modeling a workflow in an activity diagram can be done several ways; however, the following steps present just one logical process:

1 Identify a workflow objective. Ask, "What needs to take place or happen by the end of the workflow? What needs to be accomplished?" For example, if your activity diagram models the workflow of ordering a book from an online bookstore, the goal of the entire workflow could be getting the book to the customer.

2 Decide the pre- and post-conditions of the workflow through a start state and an end state. In most cases, activity diagrams have a flowchart structure so start and end states are used to designate the beginning and end of the workflow. Start and end states clarify the perimeter of the workflow.

3 Define and recognize all activities and states that must take place to meet your objective. Place and name them on the activity diagram in a logical order.

4 Define and diagram any objects that are created or modified within your activity diagram. Connect the objects and activities with object flows.

5 Define who or what is responsible for performing the activities and states through swimlanes. Name each swimlane and place the appropriate activities and states within each swimlane.

6 Connect all elements on the diagram with transitions. Begin with the "main" workflow.

7 Place decisions on the diagram where the workflow may split into an alternate flow. For example, based on a Boolean expression, the workflow could branch to a different workflow.

8 Evaluate your diagram and see if you have any concurrent workflows. If so, use synchronizations to represent forking and joining.

9 Set all actions, triggers, and guard conditions in the specifications of each model element.

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Activity Diagram-Specific Model Elements