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State Transition Diagrams Chapter 13 Another “tool” for depicting the Design An integral part of the DeSCRIPTR –State –Transition.

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Presentation on theme: "State Transition Diagrams Chapter 13 Another “tool” for depicting the Design An integral part of the DeSCRIPTR –State –Transition."— Presentation transcript:

1 State Transition Diagrams Chapter 13 Another “tool” for depicting the Design An integral part of the DeSCRIPTR –State –Transition

2 State Transition Diagram A state transition diagram is a technique to depict: 1.The states of an entity 2.The transitions of states of the entity 3.The trigger or the event that caused the transition of state of the entity The entity may be a physical device such as a light switch or a vending machine; it may be a software system or component such as a word processor or an operating system; it may be a biological system such as a cell or a human; or This modeling technique came from a more formal area called automata theory. State transition diagram depicted a Finite State Machine.

3 Software Program View The end product of a software is a program which executes. In depicting the program (or an object) we can consider: –Variables which take on different values –Control structure and assignment statements (events) in the program that change the values of the variables; but “little” is said about how the control structure or the statements work 1.Combination of values of the data (variables & constants) at any point of the program represent the program state at that point. 2. The change made to the values of the variables through assignment statements represent a transition of state

4 A very simple example light switch (page 368 of your text) Alt switchlight [l_st=on] [l_st=off] TurnOff ( ) TurnOn ( ) From State (light) To State (light) Event (switch) on turnOff off off turnOn on 1. “Sequence diagram” (alternative fragment) for switch and light interaction 2. “State transition table” for light with switch events light on light off turnOff turnOn 3. “State transition diagram” for light with switch events

5 A little “more” on the light switch off turnOff turnOn on off turnOff turnOn on What happens if we turn on a light that is already on? turnOn turnOff state can “transition” to its current state

6 Using State Transition Diagram Model the entity at the “abstraction” level where the number of states is “manageable.” 1.List (design) the states (should not be large) 2.List events that will trigger the state transition (should not be big) 3.There must be a starting state 4.There must be a terminating state or states 5.Design the transition rules (the bulk of your design work is thinking through the transition rules) 1.The above is not necessarily performed in sequence; iterate through these. 2. Even with a modest number of states and events, the state transition diagram, which really depicts the transition rules, can be enormous.

7 Designing the Voice Recorder (similar to example on page 397 of text) For the entity, voice recorder, design the states of this entity: –How many states does ( somewhat based on requirement ) a voice recorder have? Set of recorder states = { off, on, play, record, erase, stop, error-msg } –What are the initial and terminating states? Initial state = {off} Terminating state = {off} List the events that will change the state of the entity: –What are the events that will change the recorder’s states? “Input signals” = { 1, 2, 3, 4, 5, 6 } which corresponds to: { push off, push on, push play, push record, push erase, push stop} Note: no “rewind” state

8 Designing the Voice Recorder (example form page 397 of text) – cont. Design the transition rules for the voice recorder from stateto stateevents off 2 on on 1 off on 3 play erase 6 stop on 4 record on 5 erase play 6 stop record 6 stop stop 3 play stop 4 record stop 5 erase stop 1 off More transition rules: 1. Any state transition not described here will transition to error-msg state 2. once in error-msg state, the system “displays a message” and automatically transitions to stop state. off 1 off Events: {1=push off, 2=push on, 3=push play, 4=push record, 5=push erase, 6=push stop}

9 State Transition Diagram of Voice Recorder On play erase record stop Error-msg [always true] 1 4 Couple things to note: 1. All non-specified events for all the states go to “Error-msg” state is that o.k? 2. What happens when a signal of 6 comes in when in state “ON” error message? 3. How do you specify “display error message” in Error-msg state ? 4. How do you specify “Starting” and “Terminating” state ? Off Events: {1=push off, 2=push on, 3=push play, 4=push record, 5=push erase, 6=push stop}

10 UML’s “Improvements” on State Transition Diagrams Event may be expressed with a string: event-signature [guard] / action-expression State symbol may contain several compartments: Name Processing activities in the form of : Action-label / Action-expressions Action-labels: Entry – specifies activities upon state entry Exit – specifies activities upon state exit Do – specifies activities to be performed after entry but before exit Include – names another state diagram to be used for “nested” state transition diagram for further refinement Action-expression specifies the activities to be performed. Instead of include, there may be a “stubbed” state which can be expanded later. The state diagram may contain another state diagram (nested diagram) in its compartment

11 UML State Transition Composite Diagram Example (cruise control system - similar to page 401 of text) off onBtnclickoffBtnclick On pedalSpeed entry / spLock:= undefined setSpeed entry/ spLock := current speed do / lockState := on engage pressBreak freeSpeed entry / spLock := undefined do / lockState:= off exit / set offBtnclick Note: 1. the start and terminating states 2. When entering a composite diagram, the start state must be clearly defined. 3. How we exit this composite diagram from the freeSpeed state and actually enter “off” state

12 Some Deeper (Advanced) UML State Diagrams Concurrent Composite State Diagram contains two or more composite state diagrams that may be executed in parallel; state diagram is divided up into compartments by parallel dotted lines. Concurrent Composite State StateZ StateW Note: 1. Transition to a concurrent composite state boundary will enter initial states of all the concurrent state diagrams 2. Or one can specify the sub states which will be entered, along with the one specified start state 3. similarly exits can be specified Event-K Event-A

13 More Advanced UML State Transition Diagram with Synchronization Mechanism SignalOperationState EW Green NS Red EW RedEW Yellow NS YellowNS Green after 40 sec after 45 sec after 5 sec after 35 sec after 30 sec after 5 sec SynchronizedSignalOperation EW Green NS Red EW Red EW Yellow NS YellowNS Green after 40 sec after 45 sec after 5 sec after 35 sec after 30 sec after 5 sec 1 1 Synch signal used to help regulate transition Synch signal used to help regulate transition EW= east-west NS=north-south

14 Transition Junction & Compound Transition at_home on-line shopping far_away mall near_by store shopping_urge [cold=yes] [cold=no] [cold=extreme]

15 Advanced Mechanism to set History RadioOn off turnOn turnoff H Preset cd music Preset AM station Preset FM station setFM setCD setAM The history of preset state is “remembered” if the radio is turned on after it is turned off History state, H, says re-enter the state that was last active

16 Read at least one example from the text on your own. (Especially the Dialog Map and UI diagram)


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