UML Sequence Diagrams Tutorial

Study Notes

There are 3 types of Interaction diagrams: Sequence diagrams, Communication diagrams, and Timing diagrams.
These diagrams illustrate interactions between parts within a system.

Sequence diagrams model the interactions between objects in a single use case.
They illustrate how different parts of a system interact with each other to carry out a function, and the order in which the interactions occur.
Sequence diagrams are commonly used in software development to illustrate the behavior of a system or to help developers design and understand complex systems.
They can be used to model both simple and complex interactions between objects.

A sequence diagram represents a timeline that begins at the top and descends gradually to mark the sequence of interactions.
Each object has a column, and the messages exchanged between them are represented by arrows.

A sequence diagram is made up of several lifeline notations that are arranged horizontally across the top of the diagram.
No two lifeline notations should overlap each other.
Lifeline notations represent the different objects or parts that interact with each other in the system during the sequence.

A lifeline notation with an actor element symbol is used when the particular sequence diagram is owned by a use case.
A lifeline with an entity element represents system data.
A lifeline with a boundary element indicates a system boundary/ software element in a system.
A lifeline with a control element indicates a controlling entity or manager.

The activation bar is a box placed on the lifeline, indicating that an object is active (or instantiated) during an interaction between two objects.
The length of the rectangle indicates the duration of the object staying active.

An arrow from the Message Caller to the Message Receiver specifies a message in a sequence diagram.
A message can flow in any direction; from left to right, right to left, or back to the Message Caller itself.
The message arrow comes with a description, known as a message signature, on it.
The format for the message signature is: attribute = message_name (arguments): return_type.