WEEK 5 CS2002 Sequence Diagrams in UML

Software Development and Management Course

  • Brunel University LondonDr Giuseppe Destefanisgiuseppe.destefanis@brunel.ac.uk@GiuseppeDes

Introduction to UML Sequence Diagrams

  • Sequence diagrams model the interactions between objects.

  • They illustrate how messages and data are exchanged during interactions.

Structure of the Sequence Diagram

  • Horizontal Axis: Represents interaction partners (actors or systems)

  • Vertical Axis: Represents the chronological order of interactions

Key Elements

Interaction Partners

  • Depicted as lifelines:

    • Head of Lifeline: Rectangle showing role. Example: roleName:Class

    • Body of Lifeline: Dashed vertical line representing the lifetime of the interaction partner.

Exchanging Messages

  • Message Types:

    • Synchronous: Sender waits for a response before proceeding

    • Asynchronous: Sender continues immediately without waiting for a response.

    • Response message: Optional; delivered back to the sender.

  • Object creation and destruction:

    • Creation: Dashed arrow points to the new object's lifeline with the keyword new.

    • Destruction: Large cross marks the end of a lifeline.

Combined Fragments

  • Used to model various control structures in interactions.

  • Types of Operators:

    • alt: For alternative interactions (like switch)

    • opt: For optional interactions (like if)

    • loop: For repeated interactions (iterations)

    • break: For exception handling.

Types of Combined Fragment Operators

  • alt: Alternative sequences using guards to determine path.

  • opt: Optional sequence based on a guard, one operand.

  • loop: Repeated execution of an operand, specifies iterations.

  • seq: Default order of events, allows weak sequencing.

  • strict: Ensures strict ordering of messages long various lifelines.

  • par: Concurrent paths can interleave, but order of operands is irrelevant.

Practical Examples

  • alt Fragment Example:

    • Used to model different paths based on a condition, similar to switch statements.

  • loop Fragment Example:

    • Details execution with specific minimum and maximum iterations.

  • strict Fragment Example:

    • Ensures messages are passed in a precise order between interaction partners.

Notation Elements

  • Lifeline: Represents interaction partners involved.

  • Destruction Event: Indicates when an interaction partner ceases to exist.

  • Combined Fragment: Denotes different control constructs within the interaction.