2. StateChart Diagrams

3. State Machines Overview Change summary –core constructs –notation Examples Backward compatibility User benefits Issues

4. Overview State machines specify discrete behavior by mapping received events into sets of states. They may specify detailed behaviors of classes or constrain operational sequences of ports or interfaces. The core constructs in statemachines include: –States, Regions, Transitions, Events Notated using state machine diagrams Typical applications of statemachines include: –object lifecycle states an “order” object might be in –event-driven behaviors of embedded controllers –UI controllers –valid Sequences of calls via interfaces or ports

5. Change Summary for UML 2.0 New core constructs added: –entry/exit points on submachines –state machine specialization/redefinition –state machine Termination –protocol state machines transitions pre/post conditions protocol conformance UML 1.4 core constructs updated: –metamodel refactoring Notational enhancements –action blocks –state lists

6. Entry/Exit Points: Usage VerifyCard OutOfService acceptCard ReleaseCard VerifyTransaction outOfService releaseCard ATM ReadAmount : ReadAmountSM aborted usage of exit point usage of entry point rejectTransaction again invoked submachine

7. Entry/Exit Points: Definition ReadAmountSM selectAmount EnterAmount ok abort aborted amount otherAmount abort again definition of exit point definition of entry point

8. Specialization Redefinition as part of class specialization ATM acceptCard() outOfService() amount() Behaviour Statemachine FlexibleATM otherAmount() rejectTransaction() Behaviour Statemachine >

9. State Machine Redefinition State machine of ATM to be redefined VerifyCard ReadAmount selectAmount acceptCard ReleaseCard VerifyTransaction selectAmount amount outOfService releaseCard OutOfService ATM {final}

10. State Machine Redefinition FlexibleATM redefines ATM VerifyCard ReadAmount selectAmount acceptCard ReleaseCard VerifyTransaction selectAmount amount outOfService releaseCard OutOfService FlexibleATM {final} ATM {extended} EnterAmount ok otherAmount rejectTransaction {extended}

11. State Machine Redefinition FlexibleATM Statemachine States and transitions can be added States and state machines can be extended Regions can be added, and regions can be extended Transitions can be replaced or extended –Actions can be replaced –Guards can be replaced Submachines can be replaced ReadAmount SelectAmount VerifyTransaction EnterAmount ok otherAmount rejectTransaction FlexibleATM ATM {extended}

12. State Machine Specialization Independent state machine specialization –not as part of class specialization –facilitates reuse of behaviours > ATMsm > FlexibleATMsm ATMmachines

13. Protocol State Machines onGround checked flying check() [cleared for take off] takeOff() /[landing rear is retracted] land () postcondition instead of action Equivalent to pre and post conditions added to the related operations: takeOff() Pre -in state "checked" -cleared for take off Post -landing rear is retracted -in state "flying"

14. Example: Notation Enhancements Transition notationState lists Idle Req(Id) MinorReq=Id; MajorReq=Id; [ID<=10] [ID>10] Minor(Id) Major(Id) Busy alternative choice sequence of actions VerifyCard, ReleaseCard Is a notational shorthand for logCard Logged VerifyCard ReleaseCard logCard Logged

15. States example Library Title

16. Backward Compatibility In general all UML 1.4 state machine concepts are preserved in the 2.0 proposal Submachines: stub-states replaced by connection points Specialization (only a note in UML 1.4) now specified Protocol state machines now specified as a separate compliance point

17. User Benefits Entry/Exit Points –reuse via encapsulation of statemachine control interfaces –scalability Specialization –reuse, refinement Protocol State Machines –usage of stat emachines at higher level of abstraction

18. Issues State machines for operations –Currently not supported Is Event metaclass needed for state machines ? –or only part of the runtime model?

20. What Does a Statechart Depict?

21. Classifier of a State Machine The modeling element which is described by the state machine Usually a class

22. State Machines Terms and Concepts State machine is a behavior that specifies the sequences of states an object goes through during its lifetime State Event Transition

23. State Transition Diagrams Show a state machine. Emphasize the event-ordered behavior of an object. Model the changes in an object in response to the environment. Document the following: –Causes of change –Alterations in behavior based on the object’s current condition

24. StateCharts vs. Sequence & Collaboration Diagrams Sequence&Collaboration diagrams show how information passes through the objects of a system over time. State Transition diagrams show how one object changes over time, –given that methods are invoked on it by other objects. Changing the statechart states doesn’t influence the Class structure, i.e. Internal affair

25. States All objects have a “state.” The current state of any object is dictated by the values stored in its attributes. Initial final

26. States A period of time in the life of an object during which it –Satisfies some condition, and/or –Performs some activity, and/or –Waits for some events Some special states –Start state At most one –Final state Can appear many times; all have the same meaning - namely, the classifier ceases to exist

27. States initial and final substates –sequential, concurrent history states

28. States

29. Transitions Event Trigger Guard Condition Action –entry, exit, activity

30. Transitions and Events Example: statechart for Patient class A transition without an explicit event label is called trigerless When source state is complete, transition occurs

31. Events An “event” is the stimulus that prompts an object to make the transition from one state to another. Events take the form of a method call.

32. Events Trigger transitions May represent the receipt of a message: –Between system and actors –Among objects –From an object to itself Several kinds of events –Signals –Calls –Passage of time, for example: after(2 sec) –Change in state, for example: when(quantity < 10) when(date = Y2K)

33. Deferring Events EDo: UG-ban utananezni EDo: UG-ban utananezni

34. Internal Actions/Activities

35. Transition Details Guard Condition Action

36. Self- & Internal- Transitions

37. Actions Triggered by an event An executable, atomic computation Noninterruptible, runs to completion Usually the invocation of an operation (a call) –to the state machine classifier –to objects linked to the classifier

38. Actions vs. Events

39. Composite States EDo: We don’t go deeper now EDo: We don’t go deeper now

40. Sending Messages: Textual Notation

41. Sending Messages: Graphical Notation Syntax: a > dependency drawn from a transition to a class box: the dependency is labeled with the message

42. SuperStates when you have many states that respond to some of the same events in the same way

43. Overriding superstate transitions

44. Hierarchical invocation of Entry and Exit actions

45. Simple Login State Machine

46. Real world example

47. That’s it for today