CS/CPE 426 Senior Projects

1. CS/CPE 426Senior Projects Chapter 21: State Machines Chapter 22:Advanced State Machines [Arlow and Neustadt 2005] March 4, 2008

2. Outline • State machines: • Introduction • State machine diagrams • States • Transitions • Events • Advanced state machines: • Composite states • Simple • Orthogonal • Submachine states • Submachine communication • History

3. Introduction • Both activity diagrams and state machine diagrams model system behavior • However, they have different semantics: • Activity diagrams are based on Petri Nets and usually model processes when several objects participate • State machine are based on Harel’s statecharts and typically used to model single reactive objects

4. Introduction • Reactive objects: • Respond to external events • May generate and respond to internal events • Have a lifecycle modeled as a progression of states, transitions and events • May have current behavior that depends on past behavior • State machines are used to model behavior of classifiers such as classes, use cases, subsystems, systems

5. Introduction • There are two types of state machines: • Behavioral state machines • Protocol state machines • State machines are most commonly used to model dynamic behavior of classes • In UP, state machines can be used in: requirements, analysis, design • A significant challenge is testing state machines: manual walkthrough, simulation, code generation + test harnesses for state machines

6. State machine diagrams • There are three main modeling elements in state diagrams: statestransitions, and events. • Example of a simple state machine, Fig. 21.2 [Arlow & Neustadt]

7. States Summary of UML state syntax, Fig.21.4 [Arlow & Neustadt 2005]

8. Transitions Summary of UML syntax for transitions in behavioral state diagrams, Fig.21.5 [Arlow & Neustadt 2005] Where: • event(s)= internal or external occurrence(s) that trigger the transition • guardCondition = boolean expression, when true the transition is allowed • anAction = some operation that takes place when the transition fires

9. Transitions Summary of UML syntax for transitions in protocol state diagrams, Fig.21.6 [Arlow & Neustadt 2005] Note that there is no action and guard conditions are replaced by preconditions and postconditions.

10. Transitions A junction pseudo-state represents a point where transitions merge or branch, e.g. Fig.21.7 [Arlow & Neustadt 2005]

11. Transitions A junction pseudo-state may have more than one output transition (protected by mutually exclusive guard conditions) e.g. Fig.21.8 [Arlow & Neustadt 2005]

12. Transitions Choice pseudo-state can also be used, e.g. Fig. 21.9 [Arlow & Neustadt 2005]

13. Events • Events can be of four types: • Call event • Signal event • Change event • Time event

14. Events Example of a call event, Fig.21.11 [Arlow & Neustadt 2005]

15. Events A signal is a package of information sent asynchronously between objects. Example of signal event Fig. 21.12 [Arlow & Neustadt 2005] Example of sending a Signal Fig. 21.13 [Arlow & Neustadt 2005]

16. Events Change events are positive edge triggered. Example of a change event, Fig. 21.15 [Arlow & Neustadt 2005]

17. Events Time events are indicated by the keywords when and after. Example of a time event, Fig. 21.16 [Arlow & Neustadt, 2002]

18. Example of a state machine [Dascalu 2001]

19. Composite states • A composite state contains one or more nested state machines (submachines), each existing in its own region, Fig 22.2 [Arlow & Neustadt 2005]. • The composition icon is shown in Fig. 22.4

20. Simple composite states • A superstate that contains a single region is called a simple composite state, e.g.Fig 22.5 [Arlow & Neustadt 2005]

21. Orthogonal composite states • Orthogonal composite states consist of two or more sub-machines that execute in parallel. InFig 22.6 [Arlow & Neustadt 2005] there are two such composite states, Initializing and Monitoring

22. Orthogonal composite states The composite state Initializing, Fig 22.7 [Arlow & Neustadt 2005]

23. Orthogonal composite states The composite state Monitoring,Fig 22.8 [Arlow & Neustadt 2008]

24. Submachine states • A submachine state is a special state that references a state machine recorded in a separate diagram, e.g. Fig. 22. 9 [Arlow and Neustadt 2005]

25. Submachine states • Fig. 22. 10 [Arlow & Neustadt 2005]. The notation for a submachine state is <state name : name of referenced state machine diagram>

26. Submachine communication • Asynchronous submachine communication can be achieved via attributes: • The modeled reactive object has a set of attributes that can be used by submachines • The communication mechanism: one machine sets attributes and the other uses the attribute values in guard conditions of their transitions

27. Submachine communication • Example of communication via attributes, Fig. 22.11 [A&N 2005]

28. History Example of using the shallow history indicator,Fig 22.12 [Arlow & Neustadt 2005]

29. History Example of using the deep history indicator Fig 22.13 [Arlow & Neustadt 2005]