Lecture 13: Statechart Diagrams Activity Diagrams

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Lecture 13Statechart DiagramsActivity Diagrams
MIS 160 Systems Development Life Cycle I
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Object Behavior

• Help to further describes functional requirements
• Description of the actions an object performs
• Defines object responses to messages --object
  behavior

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Statechart Diagrams

• Shows all possible states for an object and the
  events that cause the object to change states
• Create a SD for every object that has clearly
  identifiable states
• Shows the (interesting) behavior of a single
  object across many use cases

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Components of Statechart Diagrams

• Always have
• States
• Events
• Transitions
• Actions
• Activities

• May also have
• Guards
• Synchronization bars
• Decision psuedostates

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Statechart Diagram Symbols
A STATE AN INITIAL STATE A FINAL
STATE AN EVENT A TRANSITION
anEvent
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States

• A condition during the life of an object
• A form or mode of being
• Satisfies a criteria
• Performs an action
• Waits for an event
• Defined by the set of values currently held by
  its attributes and by its established behaviors
• Transition
• Mechanism that causes an object to leave one
  state and change to a new state

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Event

• Something being done to the object
• Causes an object to change states
• Only 1 event can move an object from state 1 to
  state 2

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A VERY Simple Example A Printer
States
OnButtonPushed
Off
On
Transition
Event
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Actions

• Something that the object does
• Occurs in direct response (reaction) to an event
  before moving to a state
• Action-expression
• Procedural statement describing action performed
• Executes when the transition fires

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Another VERY Simple Example A Printer
Working
Load sheet Print sheet Eject sheet
OnButtonPushed
Idle
Actions
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Activities

• Associated with states
• Entry - things that happen on entry
• Exit - things that happen on exit
• Do - things that happen while in the state

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and Yet Another VERY Simple Example A Printer
Working
entry/Load sheet Do/Print sheet Exit/Eject sheet
OnButtonPushed
Idle
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Guards

• Guard condition
• A logical condition that returns only true or
  false
• Can be used for events, actions, and activities

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A VERY Simple Example A Printer
Guard
Working
OnButtonPushed Safety cover closed/statusself-
test()
Load sheet Print sheet Eject sheet
Idle
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Decision Psuedostate

• A decision point in the path of a statechart
  diagram

Working
OnButtonPushed
Load sheet Print sheet Eject sheet
Paper tray filled
Idle
Paper tray not filled
Error
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Building Statechart Diagrams

• Set the context
• Identify behaviors from your class diagram
• look at interaction diagrams and list all
  relevant input and output messages
• Identify the initial final, and stable states of
  the object
• Determine the order in which the object will pass
  through stable states
• Identify the events, actions, and guard
  conditions associated with the transitions

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Superstate and Substate

• States can be nested within states
• Superstates
• The larger (parent) state
• Substates
• Nested within the superstate
• A transition is indicated to a superstate, then
  the default substate is entered

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Example of Superstate/Substate
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Concurrent Behavior

• Objects can do multiple things in parallel
• Statechart diagrams represent concurrent behavior
  with multiple paths called threads
• Vertical bars indicate where concurrent behavior
  begins or ends

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Concurrent Substates
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Concurrent States with Synchronization Bar
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Concurrent Substate
Taking MIS 160
Proposal Accepted
Project Completed
Proposal
Project
Homework
Homework Completed
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Composite States

• A state can be decomposed
• into sequential substate
• using and-relationships into the concurrent
  substates
• using or-relationships into mutually exclusive
  disjoint substates

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OR / AND Transitions with Synchronization Bar
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Example of Sequential Substate

• e.g. research proposal and research project

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Example of Disjoint Substate

• e.g. comprehensive exam or masters thesis /
  project

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Pros and Cons of State Diagrams

• Pros
• Gives a good sense of what events should occur
  and what effects they may have on the objects.
• Gives a good overview of relationships within a
  system

• Cons
• Can get too complicated
• Difficult to visualize the behavior of the whole
  system

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Activity Diagrams
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Activity Diagrams

• Resolves the limitation of state diagrams
• State diagram is limited limits to one object and
  only shows the behavior of the object
• Activity diagram shows behavior of multiple
  objects and use cases
• Show general sequence of actions for several
  objects and use cases

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Activity Diagrams

• Activity diagrams can be used to
• model workflow
• focus on activities as viewed by actors
• often follow use case descriptions (but can be
  broader)
• model methods
• similar to flowcharts

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Activity Diagram

• Uses in connection with workflow
• Uses in describing the behavior that has a lot of
  parallel process
• Focus on flows driven by internal processing
• Each activity in the diagram is a method on a
  class

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Notation

• Synchronization bar
• Branch or Merge (Decision)

• Action State
• Transition

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Constructing Activity Diagrams

• For workflow
• determine actors
• draw in order of occurrence
• can use branches
• For methods
• determine objects
• look for computations, logic, etc.
• can use branches

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Example of Activity Diagram
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Organize Actions

• Actions may be organized into swimlanes.

• Swimlanes are a kind of package for organizing
  responsibility for activity within a class
• Arrange activity diagrams into vertical zones
  separated by lines

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Example of Swimlanes
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Action-Object Flow Relationships

• Object flow
• is shown by dashed arrows, which shows an input
  to or output by an action
• Control flow
• is shown by solid arrows, when an action produces
  an output which is an input, by a subsequent
  action. This signifies a control constraint.

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Example-actions and object flow
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State or Activity Diagram?

• If you want to look at the behavior of a single
  object across many use cases, use state diagram.
• If you want to look at behavior of multiply
  objects across many use cases or many threads,
  consider activity diagram.