1. 1 Statecharts by David Harel, 1987 State machines ⊆ statecharts A state machine consists of  Named states  Transitions between states  Events as labels on transitions State machine by itself is meaningless Must describe what states and events mean

2. 2 Statecharts by David Harel, 1987 Example: vending machine state machine Informal specification: “If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.” Formal specification by state machine” Events:

3. 3 Statecharts by David Harel, 1987 Example: vending machine state machine Informal specification: “If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.” Formal specification by state machine” Events: “quarter” = user deposited quarter

4. 4 Statecharts by David Harel, 1987 Example: vending machine state machine Informal specification: “If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.” Formal specification by state machine” Events: “quarter” = user deposited quarter “gum-button” = user pressed button for gum

5. 5 Statecharts by David Harel, 1987 Example: vending machine state machine Informal specification: “If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.” Formal specification by state machine” Events: “quarter” = user deposited quarter “gum-button” = user pressed button for gum “done” = machine finished dispensing item States:

6. 6 Statecharts by David Harel, 1987 Example: vending machine state machine Informal specification: “If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.” Formal specification by state machine” Events: “quarter” = user deposited quarter “gum-button” = user pressed button for gum “done” = machine finished dispensing item States: $X indicates that user has $X credit with machine

7. 7 Statecharts by David Harel, 1987 Example: vending machine state machine Informal specification: “If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.” Formal specification by state machine” Events: “quarter” = user deposited quarter “gum-button” = user pressed button for gum “done” = machine finished dispensing item States: $X indicates that user has $X credit with machine “dispense-gum”: machine is dispensing gum

8. 8 State Machine $0.00

9. 9 State Machine $0.00$0.25 quarter

10. 10 State Machine $0.00$0.25$0.5 quarter

11. 11 State Machine $0.00$0.25$0.5 Disp ense- gum quarter Gum button

12. 12 State Machine $0.00$0.25$0.5 Disp ense- gum quarter doneGum button

13. 13 Tracing Operation of State Machine Given an initial state and a sequence of events, How does the state machine react to the sequence of events? What state does it end up in? “Event history table” : useful tool for answering this 1.Each line contains:  Next event in sequence  State that machine is in after event 2.First line lists the initial state

14. 14 Tracing Operation of State Machine Example for the vending machine EventState -------------------------------- (start)$0.00 Quarter$0.25 Quarter$0.50 Gum-buttondispense gum Done$0.00

15. 15 Deterministic/non-deterministic “… a transition to branch at a decision point. Such an FSM is known as non-deterministic.” (p269) Comment: Not very precise … NFA – a ab

16. 16 Deterministic/non-deterministic “… a transition to branch at a decision point. Such an FSM is known as non-deterministic.” (p269) Comment: Not very precise … Still DFSM – Deci- sion a x y

17. 17 State transition matrices Example for ATM machine – withdraw StatesEvents 1.Await cardinsert card 2.Await pinenter good pin 3.Await 2 nd pin attemptenter bad pin 4.Await amountcancel 5.dispense moneyenter amount

18. 18 State transition matrices States Events

19. 19 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card 2. Await pin 3. Await 2 nd pin attempt 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense moneyenter amount done

20. 20 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin 3. Await 2 nd pin attempt 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

21. 21 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin4 3. Await 2 nd pin attempt 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense moneyenter amount done

22. 22 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin4 3. Await 2 nd pin attempt 4 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense moneyenter amount done

23. 23 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin43 3. Await 2 nd pin attempt 4 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

24. 24 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin43 3. Await 2 nd pin attempt 41 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense moneyenter amount done

25. 25 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin431 3. Await 2 nd pin attempt 41 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

26. 26 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin431 3. Await 2 nd pin attempt 411 4. Await amount 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

27. 27 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin431 3. Await 2 nd pin attempt 411 4. Await amount 1 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

28. 28 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin431 3. Await 2 nd pin attempt 411 4. Await amount 15 5. Dispense money StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

29. 29 State transition matrices CardGood pinBad pinCancelAmountDone 1. Await card2 2. Await pin431 3. Await 2 nd pin attempt 411 4. Await amount 15 5. Dispense money 1 StatesEvents Await cardinsert card Await pinenter good pin Await 2 nd pin attemptenter bad pin Await amountcancel dispense money enter amount done

30. 30 State diagram = State transition matrices

31. 31 Extending State Machines State machines simple and visual Disadvantages:  They don’t scale up well  Machine state may have to model very complex system state  May end up with confusing number of transitions  Sometimes want to express more complex conditions on transitions => Statecharts