UML stands for Unified Modeling Language and it’s a way to visualize a software system with diagrams. There exists many different types of diagrams, which are divided in two groups

  • Structural Diagrams
    • Class diagram
    • Package diagram
    • Object diagram
    • Component diagram
    • Composite structure diagram
    • Deployment diagram
    • Profile diagram
  • Behavioral Diagrams
    • Activity diagram
    • Use case diagram
    • Sequence diagram
    • Communication diagram
    • State diagram
    • Timing diagram
    • Interaction overview diagram


Activity Diagram is the UML diagram, which is taught in Programming I (IAX0583). It’s mostly used to demonstrate the logic behind an algorithm by describing each step performed by the algorithm. Activity Diagram is frequently used to Illustrate a business process or workflow between users and system.

Activity Diagram contains following main components:

  • Start – Marks start, entry point of the diagram, illustrated by solid color circle.
  • End – Illustrates end, exit point of the diagram, illustrated by circle.
  • Action – Action, which is performed by the program / algorithm. It’s illustrated by rectangle.
  • Decision – Split of control flow in two or more branches. It’s illustrated by diamond.
  • Control flow – Demonstrates the flow of the algorithm, is illustrated by arrow.

The components are demonstrated on the image below :



Usually, Activity Diagrams have single activity (control flow), start and end. It’s possible for Activity Diagram to have multiple parallel activities, entry points and exit points, but avoid using them in Programming I (IAX0583).

Another important components of an activity diagram are Swimlanes. They are used to group different actions of an activity diagram together by category or by it’s actor (Actor – The one, who performs the action). On diagram, swimlanes are either horizontal or vertical. Typical examples of swimlanes are Input, Process and Output.

Below is an example of an Activity Diagram, which describes trivial user authentication flow.



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