State Machine Diagram

Chapter 10

State Machine Diagram

• Used to describe system behavior

State Machines

• Simple set of notational elements

state-name

Initial state (pseudo-state)

State

Final state

trigger[guard]/activity

Super statetransition

Start/Final states

• Start state indicates where the state machine starts

• Final state indicates that the machine should terminate

States• Intermediate state of the system

– entry/activity: perform the activity when the state is entered

– exit/activity: perform the activity when the state is exited

– trigger/internal activity: perform the internal activity whenever trigger occurs

state-name

entry/activityexit/activitytrigger/internal activitytrigger/internal activity…

Activity state

• Think of this as a state with a separate running thread that can be interrupted at any time– As opposed to being in a “regular” state just

waiting for a trigger to arrive

– Note that a trigger[guard]/activity (next slide) cannot be interrupted

state-name

do/activity

Super state

• Just a way of grouping states to remove clutter from a diagram– When two or more states have the same

transition[guard]/activity (next slide) to the same next state you can group them together and not have to show each and every individual transition

x[y]/z x[y]/z

x[y]/z

Concurrent states• When you have multiple state machines running concurrently

(threads or multi-processing)– The history pseudo state (H) indicates the default state when entire

machine is started

H

Transition

• Cause the current state of the machine to change from state to another

– trigger: event that occurs causing the change– [guard]: condition that must be true for the change

to occur– activity: action performed as a result of the

transition

trigger[guard]/activity

Transition

• All three parts are optional– If there is no specified trigger, the state performs any

enter/exit/internal activities then leaves immediately

• Transitions out of a single state must be unique with respect to trigger[guard] specifications– Unless you want a stochastic system (randomly choose the

transition when the trigger[guard] occurs)

• Can use logical connectors (and, or, not)

Summary

• Processing begins at initial state• Proceeds to intermediate states

– Event triggered transition• Leave one state, enter the next

– Unconditional transition• Processing in the state finishes (e.g. start state)

– Concludes when the (a) final state is reached

• May be more than 1 final states

Example

Enter Password Authenticate User

characters typed <cr> typed

valid userinvalid user

Login

State Machines (cont.)

• Like everything else, state machines will be developed through a series of refinements

• The process ends when all states are “self-explanatory”

• The process results in a hierarchy of state machines

• Root node of the hierarchy is the system itself

State Machines (cont.)

• Note that these are NOT flow charts!!!– Flow charts provide a one-to-one

correspondence with code– State machines provide a one-to-one

correspondence with architectural elements

Specification Changes

Scoring

• Manual mode only

• Score counter starts at 0

• Increments by 1 each time the ball hits the paddle

• Stops incrementing when the ball moves below the paddle (game ends)

• Should be displayed at all times

Difficulty levels

• Manual mode only

• When the number of paddle hits (score) is a multiple of 10 but not a multiple of 20, increase the speed of the ball by 5%

• When the number of paddle hits (score) is a multiple of 20, decrease the size of the paddle by 5%

Score database

• When a game ends (see scoring on previous slide) have the user enter their name and save the name/score in a “database”

• Add a button to show the top 10 scores and the player names

• Add a button to show all scores for a particular player (read the player name from the user)

Deliverables

• Sequence diagram(s)

• User interface design (mock-up)

• State machine diagram for the user interface

• Revised specification

• Due two weeks from tonight– Be prepared to discuss next week