Interaction Diagrams

1
Interaction Diagrams

• Keng Siau
• University of Nebraska-Lincoln

2
Interaction Diagrams

• An interaction diagram shows an interaction,
  consisting of a set of objects and their
  relationships, including the messages that may be
  dispatched among them
• Sequence diagram
• Communication diagram

3
Interaction Diagrams

• A sequence diagram emphasizes the time ordering
  of messages
• A communication diagram emphasizes the structural
  organization of the objects that send and receive
  messages

4
Uses of Interaction Diagrams

• To visualize, specify, construct, and document
  the dynamics of a particular society of objects
• To model one particular flow of control of a use
  case

5
Contents of Interaction Diagrams

• Objects
• Links
• Messages
• Notes
• Constraints

6
Drawing Sequence Diagrams

• Place objects that participate in the interaction
  at the top of the diagram, across the X-axis
• Place the object that initiates the interaction
  at the left, and increasingly more subordinate
  objects to the right
• Place messages the objects send and receive along
  the Y-axis, in order of increasing time from top
  to bottom

7
Drawing Communication Diagrams

• Place objects that participate in the interaction
  as the vertices in a graph
• Render the links that connect these objects as
  the arcs of this graph
• Adorn these links with the messages that objects
  send and receive

8
Common Uses

• Use sequence diagrams to model flows of control
  by time ordering
• Do a better job of visualizing simple iteration
  and branching
• Use communication diagrams to model flows of
  control by organization
• Do a better job of visualizing complex iteration
  and branching and of visualizing multiple
  concurrent flows of control

9
Sequence Diagrams

• Sequence diagrams have two features
• Object lifeline
• Vertical dashed line that represents the
  existence of an object over a period of time
• Focus of control
• A tall, thin rectangle that shows the period of
  time during which an object is performing an
  action, either directly or through a subordinate
  procedure

10
Syntax for Sequence Diagram
11
Example of Sequence Diagram
12
Example of Sequence Diagram
13
Example of Sequence Diagram
14
Example of Sequence Diagram
15
Example of Sequence Diagram
16
Communication Diagram

• A communication diagram displays object
  interactions organized around objects and their
  links to one another

17
Communication Diagrams

• Dont show the lifeline of an object explicitly
• Although one can show both create and destroy
  messages
• Dont show the focus of control explicitly
• Although each messages sequence number can
  indicate nesting

18
Communication Diagrams

• Two features that distinguish them from sequence
  diagrams
• Path
• To indicate how one object is linked to another
• Sequence number
• To indicate the time order of a message

19
Communication Diagram
20
Communication Diagram
21
Communication Diagram