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.