Sequence and Collaboration Diagrams

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Sequence and Collaboration Diagrams

• University of Sunderland

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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.

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Recommended Texts

• Key text Stevens and Pooley, 2000, Using UML,
  updated edition, Addison-Wesley, ISBN
  0-201-64860-1.
• Reference text Alhir, 1998, UML in a Nutshell,
  OReilly, ISBN 1-56592-448-7. (The basis for
  much of these lectures.)
• Advanced text Graham, 2001, Object-Oriented
  Methods, 3rd edition, Addison-Wesley, ISBN
  0-201-61913-X.
• Several articles are providedexplore them
  thoroughly in tutorial and at home!

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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)

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Technique for Construction

• Specify behavior
• List class roles
• Draw lifelines
• Identify activations
• Identify messages
• Iterate

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

• Notation is a rectangle containing
  RoleNameClassName (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.

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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.,

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Activation

• Shown by a box over a lifeline
• Represents an active role
• May call itself recursively

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Messages

• 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
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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)

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Technique for Construction

• Specify behavior.
• List class roles.
• Identify association roles.
• Define message flows
• Iterate

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Sample Collaboration Diagram
A Class Role
An Anonymous Role
RoleName ClassName
ClassName
A Message
An Association Role
ClassName
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Association Roles

• Often classes
• Define the interaction between class roles.
• Multiplicities defined if the Class Roles
  represent sets of objects

Role-NameAssociation-Name
Multiplicity
Multiplicity
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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.