Sequence and Collaboration Diagrams University of Sunderland

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.

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, O’Reilly, 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 provided—explore them thoroughly in tutorial and at home!

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)

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

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

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.

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.,

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

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

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)

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

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

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

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.