StateChart Diagrams

State Machines

• Overview

• Change summary– core constructs– notation

• Examples

• Backward compatibility

• User benefits

• Issues

Overview

• State machines specify discrete behavior by mapping received events into sets of states. They may specify detailed behaviors of classes or constrain operational sequences of ports or interfaces.

• The core constructs in statemachines include:– States, Regions, Transitions, Events

• Notated using state machine diagrams• Typical applications of statemachines include:

– object lifecycle• states an “order” object might be in

– event-driven behaviors of embedded controllers – UI controllers– valid Sequences of calls via interfaces or ports

Change Summaryfor UML 2.0

• New core constructs added:– entry/exit points on submachines– state machine specialization/redefinition– state machine Termination– protocol state machines

• transitions pre/post conditions• protocol conformance

• UML 1.4 core constructs updated:– metamodel refactoring

• Notational enhancements– action blocks– state lists

Entry/Exit Points: Usage

VerifyCard

OutOfService

acceptCard

ReleaseCardVerifyTransaction

outOfService

releaseCard

ATM

ReadAmount :ReadAmountSM

aborted

usage of exit point

usage of entry point

rejectTransaction

again

invoked submachine

Entry/Exit Points: Definition

ReadAmountSM

selectAmount

EnterAmount

ok

abort

aborted

amount

otherAmount

abort

again

definition of exit point

definition of entry point

Specialization

• Redefinition as part of class specialization

ATM

acceptCard()outOfService()amount()

BehaviourStatemachine

FlexibleATM

otherAmount()rejectTransaction()

Behaviour

Statemachine

<<Redefine>>

State Machine Redefinition

• State machine of ATM to be redefined

VerifyCard

ReadAmount

selectAmount

acceptCard

ReleaseCardVerifyTransaction

selectAmount

amount

outOfService

releaseCard

OutOfService

ATM

{final}

{final}

{final}

{final}

State Machine Redefinition

• FlexibleATM redefines ATM

VerifyCard

ReadAmount

selectAmount

acceptCard

ReleaseCardVerifyTransaction

selectAmount

amount

outOfService

releaseCard

OutOfService

FlexibleATM

{final}

{final}

{final}

{final}

ATM {extended}

EnterAmountok

otherAmount

rejectTransaction

{extended}

State Machine Redefinition

• FlexibleATM Statemachine• States and transitions can be

added

• States and state machines can be extended

• Regions can be added, and regions can be extended

• Transitions can be replaced or extended– Actions can be replaced

– Guards can be replaced

• Submachines can be replaced

ReadAmount

SelectAmount

VerifyTransaction

EnterAmountEnterAmount

ok

otherAmount

rejectTransaction

FlexibleATM ATM

{extended}

{extended}

State Machine Specialization

• Independent state machine specialization– not as part of class specialization

– facilitates reuse of behaviours

<<statemachine>>ATMsm

<<statemachine>>FlexibleATMsm

ATMmachines

Protocol State Machines

onGround checked

flying

check()

[cleared for take off] takeOff()/[landing rear is retracted]

land()

postcondition instead of action

Equivalent to pre and post conditions added to the related operations:

takeOff()Pre

-in state "checked"-cleared for take off

Post-landing rear is retracted-in state "flying"

Example: Notation Enhancements

• Transition notation • State lists

Idle

Req(Id)

MinorReq=Id; MajorReq=Id;

[ID<=10] [ID>10]

Minor(Id) Major(Id)

Busy

alternativechoice

sequence ofactions

VerifyCard,ReleaseCard

Is a notational shorthand for

logCardLogged

VerifyCard

ReleaseCard

logCardLogged

Statesexample Library Title

Backward Compatibility

• In general all UML 1.4 state machine concepts are preserved in the 2.0 proposal

• Submachines: stub-states replaced by connection points

• Specialization (only a note in UML 1.4) now specified

• Protocol state machines now specified as a separate compliance point

User Benefits

• Entry/Exit Points – reuse via encapsulation of statemachine control

interfaces– scalability

• Specialization– reuse, refinement

• Protocol State Machines– usage of stat emachines at higher level of

abstraction

What Does a Statechart Depict?

Classifier of a State Machine

• The modeling element which is described by the state machine

• Usually a class

State MachinesTerms and Concepts

• State machine is a behavior that specifies the sequences of states an object goes through during its lifetime

• State

• Event

• Transition

State Transition Diagrams

• Show a state machine. • Emphasize the event-ordered behavior of an

object.• Model the changes in an object in response to the

environment.• Document the following:

– Causes of change– Alterations in behavior based on the object’s current

condition

StateCharts vs. Sequence & Collaboration Diagrams

• Sequence&Collaboration diagrams show how information passes through the objects of a system over time.

• State Transition diagrams show how one object changes over time,– given that methods are invoked on it by

other objects.

• Changing the statechart states doesn’t influence the Class structure, i.e. Internal affair

States

• All objects have a “state.” The current state of any object is dictated by the values stored in its attributes.

• Initial

• final

States

• A period of time in the life of an object during which it– Satisfies some condition,

and/or– Performs some activity, and/or– Waits for some events

• Some special states– Start state

• At most one

– Final state• Can appear many times; all

have the same meaning - namely, the classifier ceases to exist

States

Transitions

• Event Trigger

• Guard Condition

• Action– entry, exit, activity

Transitions and Events

• Example: statechart for Patient class

• A transition without an explicit event label is called trigerless

• When source state is complete, transition occurs

Events

• An “event” is the stimulus

that prompts an object to make the transition from one state to another.

• Events take the form of a method call.

Events

• Trigger transitions• May represent the receipt of a message:

– Between system and actors– Among objects– From an object to itself

• Several kinds of events– Signals– Calls– Passage of time, for example:

• after(2 sec)

– Change in state, for example:• when(quantity < 10)• when(date = Y2K)

Deferring Events EDo:

UG-ban utananezni

EDo:

UG-ban utananezni

Internal Actions/Activities

Transition Details

• Guard Condition• Action

Self- & Internal- Transitions

Actions

• Triggered by an event

• An executable, atomic computation

• Noninterruptible, runs to completion

• Usually the invocation of an operation (a call)– to the state machine classifier– to objects linked to the classifier

Actions vs. Events

Composite StatesEDo:

We don’t go deeper now

EDo:

We don’t go deeper now

Sending Messages:Textual Notation

Sending Messages:Graphical Notation

• Syntax: a <<send>> dependency drawn from a transition to a class box: the dependency is labeled with the message

SuperStates

• when you have many states that respond to some of the same events in the same way

Overriding superstate transitions

Hierarchical invocation of Entry and Exit actions

Simple Login State Machine

Real world example

That’s it for today