UML Arrows - Know UML Relationship Types

UML diagrams use different types of arrows. Each arrow type represents another relationship. Sometimes the relationships are depicted in the same way, but they have a slightly different meaning. In that case, they can be annotated with a stereotype.

UML Class Diagram Arrows and Relationships

Different arrows have different meanings in class diagrams. They represent various types of relationships.

UML class diagram arrows
UML class diagram arrows

Class diagrams use these UML arrows:

  • A triangle-head arrow with a solid line represents a generalization.
  • A triangle-head arrow with a dashed line represents a realization.
  • A circle with a plus sign represents a containment.
  • An arrow with a dashed line is used for dependencies. Except for a general dependency it may be further specialized as
    • Abstraction
    • Substitution
    • Usage
  • A solid line without any decoration represents an association.
  • An arrow with a solid line represents a directional association.
  • A double-arrowed line is used for bidirectional association.
  • An empty diamond (or white diamond) with a solid line represents a composition.
  • A filled diamond (or black diamond) with a solid line represents an aggreation.

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