An activity diagram uses symbols to represent the steps of execution. This section provides the following information about the symbols of an activity diagram:
Figure 27 shows the symbols of an activity diagram and their associated buttons in the Symbols toolbar. This toolbar becomes active when the diagram editor displays in the Working Area.
Activity diagrams contain three main types of symbols: nodes, transition links, and service calls. In addition, they contain start and end symbols.
When an activity diagram is created, a Start symbol is automatically placed in the diagram. This symbol represents the beginning of the flow; each activity diagram must have a Start symbol.
The Start symbol can be used to initialize a correlation attribute. For more information, see Using a correlation attribute.
Process Designer Express provides two end symbols for activity diagrams: End Success and End Failure. Each execution path in an activity diagram must end with one of these symbols (with the exception of an iterator activity diagram that ends with a break symbol). For more information on using the end symbols, see Terminating the execution path.
A node is a symbol that represents a step in a collaboration. There are four types of nodes: actions, decisions, subdiagrams, and iterators. Each node is represented by a unique symbol in the Symbols toolbar (see Figure 27).
Table 20 illustrates the symbol placed in the activity diagram for
each type of node.
Node type | Symbol in activity diagram | For more information |
---|---|---|
Action |
![]() | Action nodes |
Decision |
![]() | Decision nodes |
Subdiagram |
![]() | "Subdiagrams" |
Iterator |
![]() | "Iterators" |
A transition link represents control flow between nodes. Because the flow of a diagram is from top to bottom, a transition link is always oriented vertically. If multiple paths are available from a node, the transition link must be used with a decision node. Logic in the decision node determines which path is taken.
The diagram editor can represent a transition link in one of two
ways: free-form links and orthogonal links. Table 21 shows the activity diagram symbol that represents each
type of transition link.
Table 21. Transition-link symbols
Transition link type | Symbol in activity diagram | For more information |
---|---|---|
Free-form transition link |
![]() | "Transition Links" |
Orthogonal transition link |
![]() | "Transition Links" |
A service call represents a request to or response from an outside entity, through a port. It is always oriented horizontally. A service call is attached to an action node. By default, the label of a service call describes the service call type. Service calls can be one of the following:
Note that the Symbols toolbar does not contain a symbol for service calls. Service call functionality is available through the context menu that appears when you right-click an action node.
For more information on the types of service calls and how to include them in an activity diagram, see Service calls.
A symbol in an activity diagram can have the properties shown in Table 22.
Table 22. Properties of a symbol
You can edit properties of most symbols. Bring up the Symbol Properties dialog in one of these ways: