COP 4331

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COP 4331 OODP

• Lecture 9
• Object-Oriented Analysis

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Object-Oriented Analysis

• Sample problem taken from Object-Oriented
  Modeling and Design by James Rumbaugh, et.al.,
  Prentice Hall, 1991.
• Automated Teller Machine

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ATM Problem Statement

• Design the software to support a computerized
  banking network including both human cashiers and
  automatic teller machines (ATMs) to be shared by
  a consortium of banks. Each bank provides its own
  computer to maintain its own accounts and
  processes transactions against them. Cashier
  stations are owned by individual banks and
  communicate directly with their own bank's
  computers. Human cashiers enter account and
  transaction data. Automatic teller machines
  communicate with a central computer which clears
  transactions with the appropriate banks.

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ATM Problem Statement (cont.)

• An automatic teller machine accepts a cash card,
  interacts with the user, communicates with the
  central system to carry out the transaction,
  dispense cash, and prints receipts. The system
  requires appropriate recordkeeping and security
  provisions. The system must handle concurrent
  access to the same account correctly. The banks
  will provide their own software for their own
  computers you are to design the software for the
  ATMs and the network. The cost of the shared
  system will be apportioned to the banks according
  to the number of customers with cash cards.

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Identifying Object Classes

• Extract nouns from problem statement
• Eliminate spurious classes
• Candidate nouns
• Software, Banking Network, Cashier, ATM,
  Consortium, Bank, Bank Computer, Account,
  Transaction, Cashier Station, Account Data,
  Transaction Data, Central Computer, Cash Card,
  User, Cash, Receipt, System, Recordkeeping
  Provision, Security Provision, Access, Cost,
  Customer

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Identifying Object Classes.2

• Characteristics of unnecessary or incorrect
  classes
• Redundant
• Irrelevant
• Vague
• Attributes
• Operations
• Roles
• Implementation Constructs

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Identifying Object Classes.3

• Classes Eliminated
• Vague System, Recordkeeping Provision, Security
  Provision, Banking Network
• Redundant User
• Irrelevant Cost
• Attribute Account Data, Receipt, Cash,
  Transaction Data
• Implementation Access, Software

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Identifying Object Classes.4

• Remaining, Good Classes
• Account, ATM, Bank, Bank Computer, Cash Card,
  Cashier, Cashier Station, Central Computer,
  Consortium, Customer, Transaction
• Note It is sometimes necessary to add classes
  based on domain knowledge that are not part of
  the problem statement

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Identifying Associations

• Associations often correspond to stative verbs or
  verb phrases including
• Location
• Directed actions
• Communication
• Ownership
• Satisfaction of a condition

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Identifying Associations.2

• Candidate verb phrases
• Banking network includes cashiers and ATMs
• Consortium shares ATMs
• Bank provides bank computer
• Bank computer maintain accounts
• Bank computer processes transaction against
  account
• Bank owns cashier station
• Cashier station communicates with bank computer
• Cashier enters transaction for account

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Identifying Associations.2

• Candidate verb phrases (cont.)
• ATMs communicate with bank computer
• Central computer clears transaction with bank
• ATM accepts cash card
• ATM interacts with user
• ATM dispenses cash
• ATM prints receipt
• System handles concurrent access
• Banks provide software
• Cost apportioned to banks

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Identifying Associations.3

• Implicit verb phrases
• Consortium consists of banks
• Bank holds account
• Consortium owns central computer
• System provides recordkeeping
• System provides security
• Customers have cash cards
• Problem domain relationships
• Cash card accesses accounts
• Bank employs cashiers

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Identifying Associations.4

• Discard unnecessary or incorrect associations
• Associations involving eliminated classes
• Irrelevant or implementation associations
• Actions
• Derived associations
• Ternary associations
• Misnamed associations
• Role names
• Qualified associations
• Seek missing associations

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Identifying Associations.4

• Associations involving eliminated classes
• Costs, receipts, cash, system, software
• Irrelevant or implementation associations
• Concurrent access
• Actions
• Accepts cash card, Interacts with user
• Ternary associations
• Processes transaction against account
• Derived associations
• Misnamed associations
• Role names
• Qualified associations

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Adding Attributes

• Attributes are properties
• But NOT other objects
• Name
• Card code
• Password
• Cash on hand
• Date-time
• Balance

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Developing An Object Model

• Draw rectangles for objects
• Add associations
• Add multiplicities
• Revise for inheritance
• Consider further revision for simplification and
  clarity

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Use Case Diagram and Interaction Diagrams

• Develop Use Case Diagram
• Develop Example Interaction Diagram