Advanced UML State Diagrams

1. Advanced UML State Diagrams

2. Objectives • To present advanced features of the UML state diagram notation • To illustrate uses of state diagrams with advanced features • To present heuristics for making good state diagrams with advanced features

3. Topics • Concurrent composite states • Compound transitions • History and deep history states • More state diagram heuristics

4. Concurrent Composite States • The regions in a concurrent composite state nested state compartment contain state diagrams that execute in parallel. • One state in each region is entered when the concurrent composite state is entered. • One state from each region is always among the joint concurrent states until the concurrent composite state is exited. • Events cause transitions in each concurrent region to occur simultaneously.

5. Concurrent Composite State Example

6. Entering Concurrent Composite States • Make a transition to the concurrent composite state boundary • The initial state in each region becomes the current state • Make a transition to individual states in different regions • Main transition goes to a fork bar • Transitions to individual state come from the fork bar • A region without a state targeted by a transition begins in its initial state

7. Entering Selected Concurrent States: Illustration

8. Leaving Concurrent Composite States • Make a transition from the concurrent composite state boundary • For a non-completion transition, all concurrent sub-states are exited immediately • For a completion transition, the current state must be a final state in every concurrent region • Make a transition from one or more concurrent sub-states • Coordinated transitions can go to a join bar • All other sub-states are exited immediately

9. Leaving Selected Concurrent States: Illustration

10. Using Concurrent Composite States • Any concurrent composite state can be represented by a diagram with only simple states, but it will have many more states than the concurrent composite state. • Concurrent composite states thus simplify diagrams. • On the other hand, diagrams with concurrent composite states are often hard to understand.

11. Compound Transitions • Transitions from multiple sources or to multiple targets with common transition strings • Transition arrows from multiple sources may converge on a transition junction point from which a single arrow goes to a target • Common transition string stated only once • A transition arrows with a single event string may end at a junction point from which emerge arrows with mutually exclusive guards to multiple targets • Symbol is a filled circle

12. Compound Transition Example

13. History States • A history state is a pseudo-state indicating that the sub-state last active when a composite state was exited should be reentered. • Symbol is a circled H • Many common devices have persistent state, so this is a useful modeling feature.

14. History State Example

15. History State Restrictions • May only appear in a region of a composite state • Transitions may only enter a history state from outside the composite state • May have at most one unlabeled outgoing transition to a peer state • Indicates the default reentered state if the composite state has not yet been entered • History states may not have internal transitions, nested compartments, etc. • History state is forgotten if the current inner state becomes a final state.

16. Deep History States • A history state indicates reentry to a state at the same nesting level. • States at lower nesting levels are entered as usual (initial states). • A deep history state is a pseudo-state indicating that the states last active at every nesting level when a composite state was exited should be reentered. • Symbol is a circled H*

17. Deep History State Example

18. More State Diagram Heuristics 1 • Avoid concurrent composite states, especially those with synch states. • Designate an initial state in every concurrent region of a concurrent composite state. • Check that transitions to several concurrent sub-states go through a fork.

19. More State Diagram Heuristics 2 • Check that arrows connected to transition junction points are properly labeled. • Check that at most one unlabeled arrow emanates from each history state. • Check that every sequential state diagram containing a history state has an initial state.

20. Summary • State diagrams can show concurrency concurrent composite states, but these are governed by somewhat complex rules and hard sometimes hard to understand. • Compound transitions allow combination of several transitions with common transition strings into one. • History and deep history states allow state diagrams to model persistent states.