Chapter 29
State Machine Diagrams
CS6359 Fall 2011 John Cole
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State Machine Diagrams
• They show a dynamic view, the interactions
between states of an object and reaction to
events.
Telephone
initial state
off hook
Idle
Active
state
on hook
transition
event
CS6359 Fall 2012 John Cole
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Event
• A significant or noteworthy occurrence
– A telephone is taken off-hook
– A key is pressed on a keyboard
– A door is opened
– A quarter is put into a vending machine
CS6359 Fall 2011 John Cole
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Transition
• Relationship between two states that
indicates that when an event occurs, the
object moves from the prior state to the
subsequent state.
• When off-hook occurs, transition from Idle to
Active state
CS6359 Fall 2011 John Cole
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Applying the Diagrams
• If an object always responds the same way to
an event, it is state-independent or modeless.
• State-dependent objects react differently to
messages depending upon their state.
• A telephone is very state-dependent. Its
response to pushing buttons depends
whether it is on-hook or off-hook and whether
there is an ongoing call or not.
CS6359 Fall 2011 John Cole
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When to Use
• Consider state machines and diagrams for
complex, state-dependent objects, not for
state-independent objects.
• Business information systems seldom have
much state-dependent behavior (although the
UI may have some)
• Process control, device control, and telecom
have many state-dependent objects
CS6359 Fall 2011 John Cole
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Modeling State-Dependent Objects
• State machines applied in 2 ways:
– Model the behavior of a complex reactive object
in response to events
– Model legal sequences of operations such as
protocol or language specifications. A formal
grammar is a kind of state machine
CS6359 Fall 2011 John Cole
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Complex Reactive Objects
• Physical devices
• Transactions between related business
objects. How does sale, order or payment
react to an event?
• Role mutators are objects that change roles
based upon events. Person changes from
civilian to veteran. City changes from
destination to origin.
CS6359 Fall 2011 John Cole
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Protocols
• TCP can be understood with a state machine
diagram
• UI page/window flow or navigation
• UI flow controllers or sessions
• Use case system operations
• Individual UI event handling
CS6359 Fall 2011 John Cole
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Transition Actions and Guards
• Transition can cause an action. This may be
invocation of a method. Transition may also
have a test and it occurs only if the test
passes.
transition action
off hook / play dial tone
Idle
[valid subscriber]
Active
on hook
guard condition
CS6359 Fall 2011 John Cole
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Nested States
• States can have substates which inherit the
transitions of the superstate.
off hook / play dial tone
Active
[valid subscriber]
Idle
PlayingDialTone
on h
Talking
ook
digit
digit
connected
complete
Dialing
CS6359 Fall 2011 John Cole
Connecting
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