UML (Unified Modeling Language)

Common Diagram Types

Sequence Diagram

Shows the interaction between objects over time. Useful for visualizing the order of messages exchanged.

Activity Diagram

Represents workflows and processes. Shows the flow from one activity to another.

Class Diagram

Shows the static structure of a system by displaying classes, their attributes, methods, and relationships.

UML Relationships

Inheritance

Represented by a line with a hollow triangle pointing to the parent class.

Aggregation

  • External creation and usage
  • The contained object can exist independently of the container
  • Represented by a line with a hollow diamond at the container end
Container <>---- Part

Composition

  • Internal creation
  • Same lifecycle as the container
  • The contained object cannot exist without the container
  • Represented by a line with a filled diamond at the container end
Container <*>---- Part

Key Differences

Relationship Lifecycle Creation Symbol
Aggregation Independent External Hollow diamond
Composition Dependent Internal Filled diamond

References