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Notes on Class Diagrams

• Once Use Cases have initially been grouped together, then Classes need to be identified.
• Categorize classes into entity, boundary, or control.
  • Entity classes contain long term data.
  • Boundary classes interface with actors.
  • Control classes encapsulate a use case's behavior.

Class Diagram Legend

• Classes are drawn as boxes with 3 divisions:
  • (top)Class name
  • (mid)Attributes (or members, or fields)
  • (bottom)Methods (or functions)
• Arrows between Classes indicate an association
  • Numbers on each end of the line indicate Multiplicity.
    • Example: The line between Student and Enrollment has a 1 on the student side and a 1..* on the Enrollment side. This simply means that 1 Student Object can have 1 to inifinite amound of Enrollment objects. Read the other way, it means that any of many Enrollment objects can only have 1 Student object each.
  • The direction of the arrow indicates 'knowledge of.'
    • Example: Student has knowledge of Enrollment but Enrollment objects have no knowledge of Student objects.
• Text descriptions written on the Arrow help add understanding to the association.
  • Example: A Student is enrolled, via an Enrollment object, in a Seminar.