Sequence Diagrams Alternative Views

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Sequence Diagrams Alternative Views

• Prepared by Evans Adams
• January 2004

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Stereotyping Classes 1

• Entity Class
• A class whose primary focus is to hold data
• Objects of entity classes are persistent (stored
  in a database)
• Prior to developing Sequence Diagram, additional
  categories of classes are defined
• Boundary Classes
• Control Classes
• 1 - George, et. al., Object-Oriented Systems
  Analysis and Design, Prentice Hall, 2004

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Boundary Classes

• Used by Actors to interact with the system
• Forms, Dialog Boxes, Menus, Screens
• Communication with other systems
• Insulates the system from changes outside of the
  system
• Actors are only allowed to communicate with the
  system through boundary classes

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Control Classes

• Coordinate the tasks and capture the main
  application logic of a use case (or scenario)
• Insulates Entity Classes from frequently changing
  business rules
• A transaction manager for a use case (scenario)
• Directs Messages
• Enforces Business Rules
• Implements Decision Tables
• Performs Calculations

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Sequence Diagram Guidelines

• Determine Use Cases from the Use Case Diagram
• Determine the Actors which interact with the use
  case
• Do not model interactions among actors (they are
  outside the scope of the system)
• Consider one use case description at a time
• Create a Boundary Class between the use case and
  each actor (one boundary class per actor?)
• Create a Control Class for the use case
• Add the Entity Classes required by the use case
• The messages are inferred from the Flow of Events
  in the Use Case Description

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Diagramming Rules

• Actors talk only to Boundary Objects
• Boundary Objects talk only to controllers and
  actors
• Entity Objects talk only to controllers (Im not
  sure I agree with this one)
• Controllers can talk to
• boundary objects,
• entity objects and other controllers,
• but not to actors

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Example

• See Figure 9-7 Place Order Sequence Diagram

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Additional References

• IBM web site article
• IBM web site diagram

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IBM Web Site Diagram
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More Web References

• Modeling Style Guidelines
• Agile Modeling Overview

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