Chapter 5 Building Dynamic Diagrams

Flows (OOM)

A flow is a link between two activities, the route the control flow transits on between them. The routing of the control flow is made using guard conditions defined on flows. If the condition is true, the control is passed to the next element.

A flow can be created in the following diagrams:

Activity Diagram
Interaction Overview Diagram

A flow between an activity and an object node indicates that the execution of the activity puts an object in a specific state. When a specific event occurs or when specific conditions are satisfied, the control flow passes from the activity to the object node. A flow from an object node to an activity means that the activity uses this specific state in its execution. In both cases, the flow is represented as a simple arrow.

You can draw a flow from and to the following objects:

From\to	Start	Activity	OS*	Decision	Fork	Join	End
Start	—					—	—
Activity	—
ON*	—		—				—
Decision	—
Fork	—						—
Join	—
End	—	—	—	—	—	—	—

= allowed

— = not allowed *ON = Object Node

A flow can link shortcuts. A flow accepts shortcuts on both extremities to prevent it from being automatically moved when an activity is to be moved. In this case, the activity is moved and leaves a shortcut, but contrary to the other links, the flow is not moved. Shortcuts of flows do not exist, and flows remain in place in all cases.

The following rules apply:

Reflexive flows can only exist on activities
Two flows cannot be defined between the same source and destination objects (parallel flows). The Merge Model feature forbids this.

Merging models
When flows are compared and merged by the Merge Model feature, they are matched by trigger event first, and then by their calculated name. When two flows match, the trigger actions automatically match because there cannot be more than one trigger action.