What is Collaboration? • In object-oriented systems: – individual objects are responsible for only a bit of overall functionality – useful high-level behaviour (use cases) realized by objects working together – objects interact by sending messages to each other • Collaboration is: “working together for the purpose of providing some useful behaviour” – documented by collaboration diagrams BK - Spring 2006 ATM Case Study: Withdrawal Use-Case Realization Withdraw Cash ATMCustomer Withdraw Cash: The ATM customer selects the withdrawal menu, which is displayed by the system. The card holder selects an amount of cash. The system debits the user’s account, returns the user’s card and issues the requested money. BK - Spring 2006 ATM Case Study: Identifying Collaborating Classes The dashed line indicates that this class participates in the collaboration Collaboration icon Withdraw cash ATMUI CardHolder BK - Spring 2006 Debit Account CashDispenser UML Collaboration Diagrams • Collaboration diagrams involve: – Objects: instances of classes – Links: instances of associations – Actors: things/people interacting with the system • A collaboration will also usually show: – Interactions: the sequence of messages passing between objects BK - Spring 2006 UML Notation for Objects An object named user391 An anonymous object of class CardHolder user391 :CardHolder user391:CardHolder An object named user391 of class CardHolder BK - Spring 2006 Objects are notated rather like classes, but attributes and operations are omitted UML Notation for Links Links drawn as for associations. Links may have multiplicities :Account 1 0..* :Debit user391 Links are instances of associations in the class model Links represent message passing between collaborating objects BK - Spring 2006 ATM Case Study: Classes Involved in the Use Case ATMUI CashDispenser CardHolder Account Debit BK - Spring 2006 Portion of the class model involved in realizing the Withdraw Cash use case. ATM Case Study: Withdrawal Collaboration Diagram :ATMUI :CardHolder :ATMCustomer Tentative collaboration diagram for Withdraw Cash use. Note the structural similarity to the class model shown previously. BK - Spring 2006 :CashDispenser :Account :Debit Collaboration and Interaction • Individual objects have local responsibilities: – For data – For behaviour • Objects interact to achieve global behaviours: – Use case realization • Collaboration diagrams show interaction through: – Structural relationship: objects and links – Interaction: messages flowing along links BK - Spring 2006 UML Notation for Interactions Message number Message name 7: get balance() :CardHolder Messages are sent between objects along the links. BK - Spring 2006 :Account Message flow has direction of arrow ATM Case Study: Collaboration with Interaction 1:select withdrawal menu 2:select amount 3:withdraw sum :ATMUI :ATMCustomer Collaboration diagram with interactions realizing the Withdraw Cash use case :CardHolder 6:dispense sum :CashDispenser 4:debit account :Account 5:add debit :Debit BK - Spring 2006 Summary • Individual objects are responsible for small pieces of behaviour • High-level functionality is achieved through object collaboration • UML Collaboration Diagrams show: – Participating objects and links between objects – Interactions (messages sent between objects). • Stereotypes provide a mechanism for distinguishing between different sorts of object. BK - Spring 2006