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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 steps of ooa part 1
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

the steps of ooa part 2
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

ooa messages
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

a message s life cycle
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
message specification
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
syntax for message specification
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!)
slide8
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

slide9
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

slide10
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

ooa services
OOA - Services
  • exist only as elements of an object
  • services model functionality:
    • data manipulation
    • control sequences
    • communication (using messages)
    • state transformation
    • interface handling
ooa services12
OOA - Services
  • no separate graphical representation

(part of the object symbol)

  • services can be
    • public or
    • private
  • specified in the object dictionary
attributes and services
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
services and inheritance
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

slide15
Employee

Inheritance

fill-in time-sheet

prepare paycheque

Manager

Programmer

fill-in time-sheet

fill-in time-sheet

list prg-langs

scenarios
Scenarios
  • show separate self-contained sequences (threads) of execution in separate diagrams
  • include
    • objects
    • messages
    • (services)
    • (attributes)
  • do usually not include
    • structures
slide17
hire (2)

Division

create (1)

Department

Manager

Programmer

Scenario 1:

“Open a new department”

hire (3)

slide18
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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