Agenda

UML behavioral diagrams

Sequence diagrams

Behavior diagrams

Purpose

• individual aspects of a system and their changes are displayed at runtime.
• provide clarity about internal processes, business processes or the interaction of different systems.

Elements and relationships

• elements resemble verbs in a natural language
• relationships typically convey passage of time

Example

Elements of a behavioral diagram of a vehicle reservation system

• Make a Reservation
• Rent a Car
• Provide Credit Card Details.

Sequence Diagrams

How –and in what order– a group of objects works together.

Activity diagrams

Use case diagrams

Model users interacting with the system

• Users: stick figures called “actors”
• high-level overview of relationships between actors and systems
• explain system to non-technical audience

Timing diagrams

Powerful tools for making a system as efficient as possible.

• define the behavior of different objects within a time-scale
• represent objects changing state and interacting over time.

Communication diagrams

Model how components communicate and interact

Interaction Overview diagrams

Activity diagram where nodes are interaction diagrams

State Diagram

Useful for representing state machines.

• describing all possible states of objects
  • combinations of information that an object can hold
  • not how the object behaves.
• how state changes through actions/inputs

Sequence Diagrams

How –and in what order– a group of objects works together.

Use cases for sequence diagrams

Usage scenario

Draw a diagram of how your system could be used.

• ensures thinking about the logic of every usage scenario.

Method logic

Explore the logic of any function, procedure, or complex process.

Service logic

Viewing a service as a high-level method used by different clients.

Sequence diagram symbols and components

Object symbol

Lifeline symbol

Event

Actor

Alternative

Loop

• Common message symbols

Symbol	Name	Description
	Synchronous message	sender waits for response before it continues
	Asynchronous message	don’t require response before continuing. Only the call should be included in the diagram
	Create message (asyncronously)	creates a new object
	Reply message	replies to calls
	Delete message	destroys an object

Sequence diagram example

Exercise

Model (using a sequence diagram) the possible scenarios of a Customer purchasing a Product using an online shopping system:

A Customer browses/searches the Catalog, adds and/or removes Products into a Cart (updating the stocks), then goes to a Checkout page which gets its credentials from a Login (which verifies/requires that the user is logged in), allows it to select payment/shipping info, and returns to the customer an order number to allow tracking the order.