Developing Activity Diagrams (Analysis and Design)

An Activity diagram is a special form of state diagram that is used to model a sequence of behaviors and conditions taking place within the context of a workflow process. In many perspectives, Activity diagrams are similar to flow charts , except they have the capability to model parallel as well as sequential processes.

Activity diagrams can be used to examine workflow logic related to many scenarios, for example:

• Within a complex operation in an object.

• Across a single or several use case scenarios.

• Within a business process.

Activity diagrams are the perfect UML tool for depicting the flow of activities within workflow type scenarios in your system. However, they do not provide details about how objects behave or collaborate with each other, which is an important aspect of any design process. For this reason, Activity diagrams should be used in conjunction with Statechart or Interaction diagrams.

The Features of an Activity Diagram

Activity diagrams are read from top to bottom and typically consist of the following elements:

• Activities or activity states , which represent the invocation of an operation, a step in a business process, or an entire business process.

• Transitions or threads , which represent the flow of control from one activity to another through a link between the activities. A transition that involves an object is known as an object flow .

• Branches , where a transition splits into two or more mutually exclusive alternatives.

• Merger , where two or more transitions resulting from a branch combine.

• Forks , a point where a transition splits into two or more other transitions, all of which are taken. A fork is a mechanism to represent concurrent processing. This is in contrast to a branch where only one of the transitions is taken as the path to the next activity.

• Join , a point where two or more forked transitions re-join.

• Swimlanes , which represent a mechanism to group activities performed by the same organizational units.

Note

If an Activity diagram is used to model the flow of activities in a Use Case scenario, the swimlanes would identify which actor is performing the activity.

A sample Activity diagram is illustrated in Figure 3.32.

Figure 3.32. A example of an Activity diagram showcasing its elements.