Object-Oriented Analysis and Design

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1 Object-Oriented Analysis and Design Session 5: Behavioral Modeling State machine diagrams Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 1

2 2 Outline Introduction to State Machine State Machine Diagrams Syntax and Semantics State Hierarchy State History Mechanism State Concurrency Concluding Example State Machine Diagrams and UML Summary

3 Introduction to State Machine Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 3

4 Characterization of reactive systems Continuous interaction with the environment inputs and outputs are asynchronous in time. Respond to interrupts. Stringent time requirements. Multiple possible scenarios of operation, depending on the history of previous behavior. Based on interacting processes that operate in parallel. Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 4

5 Automata A machine whose output behavior is not only a direct consequence of the current input, but also of some past history of its inputs. Characterized by an internal state which represents this past experience. ON OFF Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 5

6 What are Statecharts? Statecharts are visual formalism for specifying behavior of complex systems. Developed by David Harel. Employee rest[break] Working Resting Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 6

7 7 State Machine (Automaton) Diagram Graphical rendering of automata behavior Lamp On on on off off Lamp Off

8 8 Outputs and Actions As the automaton changes state it can generate outputs: off Lamp On Lamp Off on on/print( on ) off Lamp On print( on ) off Lamp Off on on off Mealy automaton Moore automaton

9 9 Extended State Machines (1) Addition of variables ( extended state ) on ctr : Integer Lamp On on/ctr := ctr + 1 off off Lamp Off

10 Extended State Machines (2) An extended (Mealy) state machine is defined by: a set of input signals (input alphabet) a set of output signals (output alphabet) a set of states a set of transitions triggering signal action a set of extended state variables an initial state designation a set of final states (if terminating automaton) Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 10

11 State Machine Diagrams Syntax and Semantics Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 11

12 12 State Machine Diagram Initial pseudostate top top state State Trigger Ready Transition Final state Done stop/ctr := 0 stop Action

13 States Statechart Diagram Elements Any component or object within the system can be at a specific state in a given time. When holding the state, an object (or a component) can perform activities (which can be interrupted). Transitions Specification of rules for moving between states. A transition may consist of a trigger, condition, and an action. Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 13

14 14 Initial and Final States start black moves White s turn Black s turn checkmate Black wins stalemate white Draw moves stalemate checkmate White wins

15 15 Activity and Action An activity: can be performed within a state. can be continuous. can be sequential. takes time. An action: can be performed within a state or during a transition. can not be interrupted. is atomic. can take time.

16 Event-Driven Behavior Event = a type of observable occurrence interactions: object operation invocation (call event). asynchronous signal reception (signal event). occurrence of time instants (time event) interval expiry. calendar/clock time. change in value of some entity (change event). Event Instance = an instance of an event (type) occurs at a particular time instant and has no duration. Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 16

17 17 Transitions A transition is enabled if the object is at a state preceding the transition. An enabled transition is activated upon its trigger activation. S1 E1 S2 E2 S3 An initial transition indicates that the default is entering S2. A transition can connect the same state.

18 18 State Entry and Exit Actions LampOn entry/lamp.on(); exit/lamp.off(); e2 e1

Order of Actions: Simple Case Entry actions are performed

Exit actions are performed before (exiting) transition

on(); exit/printf( exiting ); off/printf( to off ); LampOff

off(); exit/printf( exiting ); Resulting action sequence:

19 Order of Actions: Simple Case Entry actions are performed after (entering) transition actions. Exit actions are performed before (exiting) transition actions. LampOn entry/lamp.on(); exit/printf( exiting ); off/printf( to off ); LampOff entry/lamp.off(); exit/printf( exiting ); Resulting action sequence: printf( exiting ); printf( to off ); lamp.off(); off/printf( needless ); printf( exiting ); printf( needless ); lamp.off(); Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 19

20 20 Internal Transitions Self-transitions that bypass entry and exit. actions Internal transition triggered by an off event LampOff entry/lamp.off(); exit/printf( exiting ); off/null;

21 State ( Do ) Activities Forks a concurrent thread that executes until: the action completes or the state is exited. Error do activity entry/printf( error! ) do/while (true) alarm.ring(); Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 21

22 22 Guards Conditional execution of transitions side-effect free bid [value < 100] /reject Selling bid [value >= 200] /sell Happy bid [(value >= 100) & (value < 200)] /sell Unhappy

23 23 Guards and Events (1) S1 E1 S2 Entered C S3 S1 E1 S2 [C] S3

24 24 Traffic Light Example N/S may go straight tm(1) [cars in N/S left lanes] N/S may turn left tm(1) tm(1)[no cars in E/W left lanes] tm(1)[no cars in N/S left lanes] tm(1) E/W may turn left tm(1)[cars in E/W left lanes] E/W may go straight

25 25 Phone Line Example on hook on hook Busy tone do: sound busy tone digit (n) on hook on hook busy on hook / disconnect line on hook Idle Dial tone do: sound dial tone Dialing Ringing Connected Disconnected off hook digit (n) valid number Connecting do: find connection routed time out time out on hook invalid number called phone answers / connect line called phone hangs up / disconnect line Time out Recorded message do: play message message done

26 26 Static Conditional Branching Merely a graphical shortcut for convenient rendering of decision trees. Selling Happy bid [value < 100] /reject [value >= 200] /sell [(value >= 100) & (value < 200)] /sell Unhappy

27 27 Dynamic Conditional Branching Choice pseudostate: guards are evaluated only when the decision point is reached. Selling Happy bid /gain := calculatepotentialgain(value) [gain < 100] /reject [gain >= 200] /sell Dynamic choicepoint Unhappy [(gain >= 100) & (gain < 200)] /sell

28 State Hierarchy Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 28

29 States Hierarchy (1) Intended to cluster together alternative states of a single aspect / object. Results: OR states. An OR state is a super-state of its sub-states. A state that has no sub-states is a basic state. Indentation-status On The states in an IndentationStatus statechart: Off Left Right Center Justify Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 29

30 30 States Hierarchy (2) States hierarchy is used for describing different levels of abstraction. High Level Detailed Level

31 31 States Hierarchy (3) States hierarchy is used for clustering. Un clustered clustered

32 States Hierarchy (4) Initial States one per state. To be in a state is to be in ONE of its sub states. Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 32

33 33 States Hierarchy (5) Graduated attack on complexity states decomposed into state machines off/ LampOff entry/lamp.off() flash/ LampFlashing FlashOn entry/lamp.on() LampOn on/ entry/lamp.on() on/ on/ 1sec/ 1sec/ FlashOff entry/lamp.off()

34 34 States Hierarchy (6) Higher-level transitions Default transition to the initial pseudostate LampOff entry/lamp.off() off/ on/ LampOn entry/lamp.on() flash/ on/ LampFlashing FlashOn entry/lamp.on() 1sec/ 1sec/ FlashOff entry/lamp.off()

35 35 States Hierarchy (7) Triggered by a completion event generated automatically when an immediately nested state machine terminates. Committing Phase1 completion transition (no trigger) Phase2 CommitDone

36 States Hierarchy (8) Two or more transitions may have the same triggered event inner transition takes precedence. if no transition is triggered, event is discarded. LampFlashing FlashOn on/ off/ FlashOff on/ Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 36

37 37 States Hierarchy (9) Same approach as for the simple case S1 exit/exs1 S11 exit/exs11 E/actE S2 entry/ens2 inits2 S21 entry/ens21 Actions execution sequence: exs11 exs1 acte ens2 inits2 ens21

38 State History Mechanism Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 38

39 History Mechanism (1) Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 39

40 History Mechanism (2) Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 40

41 41 History Mechanism (3) G

42 History Mechanism (4) Return to a previously visited hierarchical state deep and shallow history options suspend/ Diagnostic1 Diagnosing Diagnostic2 Step11 Step21 resume/ H* Step12 Step22 Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 42

43 State Concurrency Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 43

44 44 Orthogonality and Concurrency (1) Multiple simultaneous perspectives on the same entity age employee Child Adult Staff Member Retiree Manager

45 45 Orthogonality and Concurrency (2) Describe independent components of a behavior. Behavior of parts of an aggregate object. Enforce synchronization of concurrent activities. Concurrency is an AND-decomposition of a state. To be in a state S is to be in ALL of its components. S is an AND state.

46 46 Orthogonality and Concurrency (3) Combine multiple simultaneous descriptions age employee Child Adult age employee Staff Member Retiree Child Adult Staff Member Manager Retiree Manager

47 Orthogonality and Concurrency (4) A a B C b (in G) D g E G d a m F Use of Orthogonal Regions B,E m g B,F d B,G No Use of Orthogonal Regions a C,E m g C,F a a d a b C,G Object-Oriented Analysis and Design 47

48 48 Orthogonality and Concurrency (5) All mutually orthogonal regions detect the same events and respond to them simultaneously. legalstatus financialstatus LawAbiding Poor Outlaw robbank/ Rich robbank/

49 49 Orthogonality and Concurrency (6) Typically through shared variables or awareness of other regions state changes. sane : Boolean Catch22 sanitystatus flying : Boolean flightstatus request Grounding/ Crazy entry/sane := false; (flying)/ Sane entry/sane := true; Flying entry/flying := true; (~sane)/ Grounded entry/flying := false; (sane)/

50 Transition Sequence A transition might be a trigger An event can trigger additional transitions Several transition can be triggered within a single step Solution The number of triggered transition should be limited A C b/d a/c d/a c/b B D Object-Oriented Analysis and Design 50

51 51 Transition Forks and Joins For transitions into/out of orthogonal regions: age Child Adult Retiree Staff Member Manager employee

52 Reducing Multiple Transitions (1) Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 52

53 Reducing Multiple Transitions (2) Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 53

54 Concluding Example Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 54

55 55 Mini Organ Example (1) ON\OFF a Display STYLE b Name Mode SONG c Number START

56 56 Mini Organ Example (2) 1. The button a is used for switch the organ on and off 2. The organ enables a song selection and its style. When the organ is turned on the display shows the mode: STYLE or SONG and its number. The default is song #1/sytle #1 and the mode is STYLE. 3. To select a style one need to press the b button and the required style number (1-9). Each style has a function that return its name StyleName(x). 4. To select a song one need to press the c button and the required song number(1-9). Each song has a function that return its name SongName(x). 5. Pressing the start button plays the current song following the current style. Another press stop the music. It is possible to change the song or style during music playing.

57 57 Mini Organ Example (3) Events a - pressing the a button b - pressing the b button c - pressing the c button s - pressing the START button i - pressing the a digit button (2-9) 1 - pressing the 1 button songend end of song playing Variables i,j can get values between 2-9 k,m can get values between 1-9 w can get a song or style name

58 58 Mini Organ Example (4) off a a on play mode song# style# display s or songend disable enable s Do: if song# in k and style# in m then play song k in style m style b song c 1[c1] j[c1] 1 j i[c2] 1 i 1[c2] disp-mode x style name [c4] b w [c2] c [c1] song number k y [c3]

59 State Machine and UML Mira Balaban & Arnon Sturm Object-Oriented Analysis and Design 59

60 60 Dishwasher Class Diagram Dishwasher cycles : int rinsetime : int washtime : int drytime : int Tank evtankdrain() evtankfill() 1 itstank Dishwasher() setup() evstart() evopen() evclose() evquick() evnormal() evintensive() evservice() 1 itsjet Jet evjetoff() evjetspray() evjetpulse() itsheater 1 Heater evheateroff() evheateron()

61 61 Dishwasher State Machine Diagram AcmeHeater AcmeJet Dishwasher off evheateron evheateroff idle on evjetspray evjetoff evjetpulse AcmeTank evtankfill tm(4000)/ itsdishwasher->gen(evfull); filling running spraying pulsing empty> full> tm(4000)/ itsdishwasher->gen(evempty); draining evtankdrain

62 62 Summary UML uses a variant of Harel s statecharts adjusted to software modeling needs Used to model event-driven (reactive) behavior well-suited to the server model inherent in the object paradigm Includes a number of sophisticated features that realize common state-machine usage patterns: entry/exit actions state activities dynamic and static conditional branching Also, provides hierarchical modeling for dealing with very complex systems hierarchical states hierarchical transitions orthogonality

State modeling. Marlon Dumas. Institute of Computer Science

State modeling. Marlon Dumas. Institute of Computer Science State modeling Marlon Dumas Institute of Computer Science Where are we? Notation Class diagrams Use case diagrams/use cases Sequence diagrams Statecharts Petri nets Decision trees & DMN Purpose Domain