State Diagrams

Business process models do not lend themselves to implementation in an object-oriented way. If you go the UML way, you will break down the business process and express it in terms of states for each object involved in the process. State diagrams are used to illustrate the possible states of an object and the causes and effects of those state changes within the object.

Let's take a short look at the States themselves. In the diagram toolbar you find three different symbols:

• State

  In a state diagram, each state has at least two compartments, the top one always keeping the name of the state. The name usually is an adjective describing the recent object.

  The states properties are a lot more meaningful and complex than they are in the activity diagrams. Not only does a state have ingoing and outgoing transitions, but also different actions or activities that are to be taken with it.

• Composite State

  Composite States make visual use of the second compartment that encloses refinements of the given state. Enclosed states don't have to have an initial state. Ingoing as well as outgoing transitions might be connected directly to one of them. When the corresponding object is in the composite state, it is exactly in one of the sub-states (OR relation).

  If you find yourself needing to change a simple state to a composite state, you have to delete the former and again add the new state via the toolbar.

• Concurrent State

  Concurrent States are, like the above, refinements; therefore, they are focused in the second compartment. When the corresponding object enters the concurrent state, all initial sub-states all are enabled at once (AND relation).

Editing States

Actions and activities are added from within the state's Property tab using the 'Add' button. Whenever you add an action or activity, Poseidon will automatically navigate to the new element. Upon return to the parent element, the 'Add' button will no longer be visible, rather it will be the 'Delete' button, indicating that the element has been successfully added.

To remove an existing element, use the 'Delete' button. Note that this will delete the element entirely from the model.

Some items within the Property tab will appear in blue - these are in effect hyperlinks to the element. Clicking on them will navigate to the element named.

Editing Actions and Activities

Actions and Activities are elements in themselves, just like any other part of the model. As such, editing them is done in the same way as any other element - just like an attribute is a part of a class.

For more information about the specific fields, see the Element section the Section called States in Chapter 12.