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The OOA Process - II

The OOA Process - II. Scenarios. The Steps of OOA - Part 1. identify objects (classes) identify structures generalization - specialization (“ISA”) whole - parts (“PART-OF”) association (relationship) define attributes ===> Static Objectdiagram ===> incomplete Object Dictionary.

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The OOA Process - II

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  1. The OOA Process - II Scenarios

  2. The Steps of OOA - Part 1 • identify objects (classes) • identify structures • generalization - specialization (“ISA”) • whole - parts (“PART-OF”) • association (relationship) • define attributes ===> Static Objectdiagram ===> incomplete Object Dictionary

  3. The Steps of OOA - Part 2 • define services via scenarios • services per object • message passing between objects • coordination of message passing • states and transitions ===> Scenarios ===> complete Object Dictionary

  4. OOA - Messages sender • form the dynamic portion of the object diagram (scenarios) • sent by • an object (instance) • via an active local service • received by • an object (instance) • triggering the receiving service label receiver

  5. A Message’s “Life-Cycle” • connects to an object(object_id).service • triggers execution of the receiving service • carries input-parameters for the execution of the receiving service • is able to transmit output-parameters back to the sending service

  6. Message Specification • scenarios (diagrams): • shown as bold or dotted line • label is optional • parameters are optional • sequence number is optional • object dictionary: • exist only as elements of an object’s services • specified as part of the service specifications

  7. Syntax for Message Specification • typically similar to: SEND MESSAGE TO object (object_id).service (input-parameters, output-parameters) • object: name of an object class • service: name of a service in that object class • object_id: identifies selected instantiation (structures, especially associations!)

  8. The division wants to compile a list of the prg. languages “spoken” in its departments. Division (2,N) (1,1) Programmer Department list of prog-lang. (1,1) (3,N) works-for

  9. Division Alternative 1: Using output-parameters to get to the results. report prg-langs list prg-skills (wait for result) Programmer Department list prg-lang (wait for result) list prg-lang list prg-skills

  10. Alternative 2: Using separate messages to transmit results. Division report prog-langs accept prg-lang accept prg-lang list prg-skills (do not wait for result) Programmer Department list prg-lang (do not wait for result) list prg-langs list prg-skills

  11. OOA - Services • exist only as elements of an object • services model functionality: • data manipulation • control sequences • communication (using messages) • state transformation • interface handling

  12. OOA - Services • no separate graphical representation (part of the object symbol) • services can be • public or • private • specified in the object dictionary

  13. Attributes and Services • the data capsule principle • a service has access to all attributes of the local object • all services of an object share attributes as a global data area • a service provides access to attributes for other object.services (by accepting messages) • a service can have local variables

  14. Services and Inheritance • are inherited in a classification hierarchy • inheritance is mandatory • multiple inheritance is possible => position common services as high in the classification hierarchy as possible => generic services / service overlay / polymorphism

  15. Employee Inheritance fill-in time-sheet prepare paycheque Manager Programmer fill-in time-sheet fill-in time-sheet list prg-langs

  16. Scenarios • show separate self-contained sequences (threads) of execution in separate diagrams • include • objects • messages • (services) • (attributes) • do usually not include • structures

  17. hire (2) Division create (1) Department Manager Programmer Scenario 1: “Open a new department” hire (3)

  18. Scenario 2 (Alternative 2): “Prepare list of prog. languages for divison.” Division report prog-langs accept prg-lang accept prg-lang list prg-skills (do not wait for result) Programmer Department list prg-lang (do not wait for result) list prg-langs list prg-skills

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