Relationships in Use Case Diagram

Relationships:

  • Association:
  • An association is a relationship between two objects that are link or combined with each other.
  • This can be a “IS-A” or “IS-Many” relationship between two objects which shows some kind of relationship between “One-to-one” or “One-to-Many” objects.
  • Representation:

It is usually drawn as a Solid Line connecting two objects.

  • Association can be of two types: Aggregation & Composition.
  • Aggregation:
  • It is a “Has-A” or “Has-Many” relationship.
  • Representation:

It is represented by an Unfilled Diamond arrow, which should point towards dependency.

  • Composition:
  • Composition implies “Ownership”, the Lifetime of an object is dependent on another object’s existence.
  • Representation:

It is represented by a Filled Diamond arrow, which should point towards dependency.

  • Include:
  • Include is a path in action and it’s Compulsory.
  • Here Parent Class Action is dependent on Child Class Action.
  • Representation:

It is represented by an Arrow and that arrow’s direction should be towards dependency.

  • Extend:
  • Extend means Optional – may or may not.
  • Here Parent Class Action is not dependent on Child Class Action.
  • Representation:

It is represented by an Arrow and that arrow’s direction should be towards dependency.

  • Generalization:
  • This is also an also a parent-child relationship where Parent Class doesn’t exist without none of Child Classes.
  • Representation:

It is represented by an Arrow and that arrow’s direction should be towards dependency.

  • There are two types of Generalization: Actor Generalization and Use Case Generalization.

Representation of Actor and Use Case Generalization:

It is represented by an Unfilled Triangle arrow, which should point towards dependency.

  • Actor Generalization:
  • It shows the dependency between two Primary Actors.
  • Use Case Generalization:
  • It shows the dependency between two or more Child use cases with a Parent Use Case.

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