1 Statecharts by David Harel, 1987 State machines ⊆ statecharts A state machine consists of Named...
31
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
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Transcript of 1 Statecharts by David Harel, 1987 State machines ⊆ statecharts A state machine consists of Named...
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 meaninglessMust describe what states and events mean
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Statecharts by David Harel, 1987
Example: vending machine state machineInformal specification:“If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.”
Formal specification by state machine”Events:
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Statecharts by David Harel, 1987
Example: vending machine state machineInformal 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
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Statecharts by David Harel, 1987
Example: vending machine state machineInformal 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
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Statecharts by David Harel, 1987
Example: vending machine state machineInformal 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 itemStates:
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Statecharts by David Harel, 1987
Example: vending machine state machineInformal 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 itemStates:$X indicates that user has $X credit with machine
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Statecharts by David Harel, 1987
Example: vending machine state machineInformal specification:“If user deposits two quarters and presses button for gum, a pack of gum will be dispensed.”
Formal specification by state machine”Events: “quarter” = user deposited quarter“gum-button” = user pressed button for gum“done” = machine finished dispensing itemStates:$X indicates that user has $X credit with machine“dispense-gum”: machine is dispensing gum
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State Machine
$0.00 $0.25 $0.5
Dispense-gum
quarter quarter
Gum button
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State Machine
$0.00 $0.25 $0.5
Dispense-gum
quarter quarter
done Gum button
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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 sequenceState that machine is in after event
2.First line lists the initial state
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Tracing Operation of State Machine
Example for the vending machine
Event State--------------- -----------------(start) $0.00Quarter $0.25Quarter $0.50Gum-button dispense gumDone $0.00
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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
a b
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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
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card
2. Await pin
3. Await 2nd
pin attempt
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin
3. Await 2nd
pin attempt
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4
3. Await 2nd
pin attempt
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4
3. Await 2nd
pin attempt4
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3
3. Await 2nd
pin attempt4
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3
3. Await 2nd
pin attempt4 1
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3 1
3. Await 2nd
pin attempt4 1
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3 1
3. Await 2nd
pin attempt4 1 1
4. Await amount
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3 1
3. Await 2nd
pin attempt4 1 1
4. Await amount
1
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3 1
3. Await 2nd
pin attempt4 1 1
4. Await amount
1 5
5. Dispense money
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State transition matrices
Card Good pin Bad pin Cancel Amount Done
1. Await card 2
2. Await pin 4 3 1
3. Await 2nd
pin attempt4 1 1
4. Await amount
1 5
5. Dispense money
1
States EventsAwait card insert cardAwait pin enter good pinAwait 2nd pin attempt enter bad pinAwait amount canceldispense money enter amount
done
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State diagram = State transition matrices
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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
