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.