1. Sequence and Collaboration Diagrams
University of Sunderland

2. Purpose
Used to describe how subsystems and objects interact to produce the behavior of the system.
Provide complementary representations of the same information. You can convert from sequence diagrams to collaboration diagrams by considering the association roles.
Collaboration diagrams are the starting point for generating the object and class diagrams.
Collaboration diagrams are renamed communication diagrams in UML 2.

3. Recommended Texts
Key text: Stevens and Pooley, 2000, Using UML, updated edition, Addison-Wesley, ISBN
Reference text: Alhir, 1998, UML in a Nutshell, O’Reilly, ISBN: (The basis for much of these lectures.)
Advanced text: Graham, 2001, Object-Oriented Methods, 3rd edition, Addison-Wesley, ISBN X.
Several articles are provided—explore them thoroughly in tutorial and at home!

4. Sequence Diagram Notation
Sequence diagrams contain the following:
Class roles (subsystem/object/class, actor, and external system roles in the interaction). These are (usually) drawn across the top of the diagram.
Lifelines (subsystem/object/class existence). These (usually) extend down the diagram.
Activations (show when the subsystem/object/class is doing something)
Messages (communication between roles)

5. Technique for Construction
Specify behavior
List class roles
Draw lifelines
Identify activations
Identify messages
Iterate

6. Sample Sequence Diagram
Role1
Role2
Role3
Role4
Class Role
Activation
Message
Lifeline
Recursive Activation

7. Class Roles
Notation is a rectangle containing RoleName:ClassName (both underlined)
Can be an interface instead of class.
May have a number in the upper right hand corner giving the number of instances involved.
Represents an object, class, actor (person), subsystem or external system.

8. Lifelines
Dashed or dotted line from past to future or from birth to death if a role with a limited lifespan.
Death is marked with a large
May split and merge to represent alternative paths. E.g.,

9. Activation Shown by a box over a lifeline Represents an active role
May call itself recursively

10. Messages } paired Denoted by labeled horizontal arrows
If simply an arrow, represents flow of control.
If shown as:
represents a handshake (e.g., TCP).
If with a half-arrowhead, asynchronous (e.g., UDP):
If at an angle rather than horizontal, represents a time delay:
} paired

11. Collaboration Diagram Notation
Forms a context for interactions
May realize use cases
May be associated with operations
May describe the static structure of classes
Collaboration diagrams contain the following:
Class roles (subsystems/objects/classes/actors/ external systems) as before.
Association roles (pathways or links over which messages flow)
Message flows (messages sent between class roles)

12. Technique for Construction
Specify behavior.
List class roles.
Identify association roles.
Define message flows
Iterate

13. Sample Collaboration Diagram
A Class Role
An Anonymous Role
RoleName: ClassName
:ClassName
A Message
An Association Role
:ClassName

14. Association Roles Often classes
Define the interaction between class roles.
Multiplicities defined if the Class Roles represent sets of objects
Role-Name:Association-Name
Multiplicity
Multiplicity

15. Message Flows
Sequence numbers on every message. These can be nested to associate related messages.
Arrows are the same as those used in sequence diagrams.