Poseidon for UML: Users Guide
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# Activity Diagrams

Activity diagrams are often used to model business processes. They simply and quite plainly show how things work, and so function as a good aid to discussions of aspects of the workflow with the domain experts. These are less abstract than the often used object-oriented state diagrams.

The following example shows an activity diagram that depicts the rules and the process of paying an order. In the following example, `Softsale` will not accept an order if you have overdue payments open, will only allow payment by invoice if your e-mail and home address have been verified, and a few other rules. Take a closer look for yourself in order to become more familiar with the notation.

Figure 10-3. An Activity diagram.

## Diagram Elements

- Initial States and Final States - Indicate the beginning and end of the observed process.

- Action States - Specific activities which comprise the process. They must be executed in a specified chronological order. Sometimes you may want to split the sequence; therefore, you have two different possibilities: Branches (choice) and Forks (concurrency).

- Branches - These divide the sequence into several alternatives specified by different conditions (guards).

- Forks and Joins - Forks divide the sequence into concurrent sub-sequences. Joins merge the sub-sequences.

- Synchronization States - Used in concurrent sub-sequences to synchronize producer-consumer relations.

- Transitions - The ingredient that keep states active and the model elements together. Each transition can be given guards , triggers , and actions as properties to describe its behavioral details.

- Object Flow States - Objects are inputs or outputs of activities and are accordingly connected by transitions to them.

- Dependencies - Always possible between any model elements.

## Toolbar

| Select
| Action State
| Object Flow State
| Transition
| Initial State
| Final State
| Synchronization State
| Branch
| Fork
| Join
| Note
| Connect Comment to Element
| Text
| Circle
| Rectangle
| Polygon
| Polyline
| Repaint

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