Behavioral diagramsBehavioral diagramsLectureLecture

p4p4T120B029T120B029

20201212 pavasario sem. pavasario sem.

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State diagrams

• Positioning in development process• Basic definitions and symbols• Notations• Examples• Remarks• Concurrency• Events, signals, exceptions

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Main processes of the team assignment

requirementsanalysis

designprocess

coding testing

Used technique:UML use case diagramsUML activity diagrams

Used technique:UML component diagrams,UML class diagrams, UML state diagramsUML sequence diagrams,UML activity diagrams

Used languages:JavaC++

…

requirementsdocument

problem description

design document

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Refined design processes of the team assignment

requirementsanalysis

designprocess

coding testing

create systemarchitecture

specify componentinterfaces

develop component design

Used technique:UML class diagrams, UML state diagramsUML sequence diagrams,UML activity diagrams

Used technique:UML component diagrams

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State diagrams• Shows the behavior of one object of a

single class– shows all possible states of this object– shows how the object’s state changes as a

result of messages it receives– narrowly focused, fine-grained

• Other names– State transition diagram– Harel diagram (statecharts)

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Object states• State

= set of values that describe an object (its condition/situation) at a specific moment in time

• State is determined based on the attribute values

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Account

balance : Float states

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State changes (1)• States may be

changed when an event occurs

• State transition: relationship indicating a state change – atomic (i.e. non-

interruptible)

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deposit(sum) withdraw(sum)

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State changes (2)• Events: Messages or signals

received• Events may or may

not change the state– Self-transition

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deposit

withdraw

deposit

withdraw

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State diagram notation:for one state

• Activity: Can take longer and can be interrupted

• Action: Occurs quickly– “quickly” = non-interruptible– entry: an action that is performed on entry

to the state– exit: an action performed on exiting the

state

• do: an ongoing activity performed while in the state (example: display window)

• on: an action performed as a result of a specific event– Different from self-transition

State name

entry / entry-action

exit / exit-action

do / activity-Aevent1(a:T)[exp]: action1

state variable(s)

eventn(a:T)[exp]: actionn

…

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State-A State-BEvent(arguments)[condition]/action

State diagram notation:from one state to another

• Event: significant occurrence that has a location in time and space– triggers the transition– signals, calls, passing of time, change in state

• Guard condition: • Transition only occurs when guard evaluates to true• Guards of transition exiting one state are mutually

exclusive• Action: Processes considered to occur quickly and are

not interruptibleNote: Each part can be omitted!

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State diagram notation:special states

• Start state– No event triggers allowed – branch conditions allowed– may not remain in start state

• End state– Top level end state terminates a state machine

Initial state State-BEvent(attribute)

Start State End State

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Let us look at anexample of Statechart

Diagrams :Order Management

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State transitions for an order

Checking

do: check item

Dispatching

do: initiate delivery

Waiting

Delivered

/ get first item

Item received [ some items not in stock ]

Item received[ all items available ]

Delivered

[ All items checked && some items not in stock ]

[ All items checked && all items available ]

[ not all items checked ] / get next item

Event

Guard

Action

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Problem: Cancel the order

• Want to be able to cancel an order at any time

• Solutions– Transitions from every state to state

“cancelled”– Superstate and single transition

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Transitions to “cancelled”

Dispatching

do: initiate delivery

Waiting

Delivered

Item received[ some items not in stock ]

Item received[ all items available ]

Delivered

Cancelled

Checkingdo: check

item

[ not all items checked ] / get next item

/ get first item

[ All items checked &&some items not in stock ]

[ All items checked && all items available ]

cancelled

cancelled

cancelled

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State diagram notation:structuring diagrams (1)

Superstate

State-A State-BState-A State-BEvent A

Event B Event C

Composite state:Sequential substates

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Superstate / Substates

Dispatching

do: initiate delivery

Waiting

Delivered

Item received[ some items not in stock ]

Item received[ all items available ]

Delivered

Cancelled

Checkingdo: check

item

[ not all items checked ]/ get next item

/ get first item

[ All items checked && some items not in stock ]

[ All items checked && all items available ]

Active

cancelled

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State diagram notation:structuring diagrams (2)

Superstate

State-A State-BState-A State-BEvent A

Event B Event C

H

History stateStart with the last substatethat was active prior to leaving the composite state

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Another example:Icehockey with superstate

Normal

playing

break

Fighting

end of game

shootout

penalty

face off

time is uo [win ]

time is up [tie]

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Remarks (1)

• Statechart diagrams do not have to refer to classes or objects, they can also refer to subsystems etc…

• However, often describing classes is the most widely use of statechart diagrams...

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Remarks (2)• Only one initial state may occur

(directly) within a composite state• End state represents completion of

a composite• End state triggers transition with

composite as source

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Orthogonal components and concurrency

• Unrelated components of objectscombinatorial number of states

• Example: Car states– engine (started, stopped)– doors (open, closed)

• What happens when we add one component?– seat belt (fastened, open)

4 car states:started_openstarted_closedstopped_openstopped_closed

8 car states:started_open_open started_open_fastenedstarted_closed_open started_closed_fastenedstopped_open_open stopped_open_fastenedstopped_closed_open stopped_closed_fastened

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Example: Payment authorization in class

Order

Authorizing

do: check payment

Authorized

Delivered

Rejected

[ payment ok ]

[ payment not ok ]2 parallel processes:- authorization- order handling

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Concurrent state diagram for the class

Order

Checking

Waiting

Dispatching

Authorizing Authorized

Checking

Waiting

Dispatching

Authorizing Authorized

Cancelled

Delivered

Rejected

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Rules of thumb

• Not every class needs a state diagram• Often: State diagram not very complex• State diagrams are often used for UI

and control objects• Not too many concurrent sets of

behavior occurring in a single object (in that case: split into separate objects)

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Proposed Exercises• Define a statechart diagram for

– a hockey game– an elevator– a soccer game– …

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