Activity edges in activity diagrams

In activity diagrams, an activity edge is a directed connection between two activity nodes. When a specific action in an activity is complete, the activity edge continues the flow to the next action in the sequence.

You can use two types of activity edges to model the flow in activities:

Control flow edges model the movement of control from one node to another.
Object flow edges model the flow of objects or data from one node to another.

Typically, activity edges do not have names; however, you can add a name to describe the purpose of each edge.

As the following figure illustrates, an activity edge is displayed as a solid line with an open arrowhead that points in the direction of the flow.

An activity node connected by an arrow to another activity node

Tip: You can specify a default style for the edges that you add to activity diagrams in the Preferences window, on the Activity Diagrams page.

Guard conditions on activity edges

You can add a guard condition to an activity edge between two nodes, where the guard condition defines a condition that must be satisfied before the target activity node can be invoked. You can define the guard condition in the following ways:

name [guard condition] - The guard condition is created and is assigned a name.
[guard conditon] - The guard condition is created, but is not assigned a unique name.

In the following figure, one activity node called OpaqueAction is connected to a second activity node, called OpaqueAction2. A guard condition, called Guard1, specifies that the value of g coming from OpaqueAction must be greater than 10 for OpaqueAction2 to be invoked.

Two activity nodes connected by an activity edge with a guard condition