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Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
Unit 4
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Unit 4

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  • 1. Unit 4Object Oriented design process and design axioms
  • 2. Object Oriented design process Access layer •Create mirror class •Identify access layer class relationship •Simplify class and relationship •Remove redundant class •Method class Design Apply design User calsses, axioms Design view / satisfaction methods, Refine UML access layers and usability attributes, classDiagrams and prototype test based onassociations use cases
  • 3. Object Oriented design axioms• Axioms – Hypothesized from observation – Common truth – Always valid – No need to prove and derive• Theorem – It can be proven from axioms• Corollary – Follows from axioms and theorems
  • 4. Axioms for OOAD• Axiom1 – Maintain the independence of component • While going from requirements and use case to system component, each component must satisfy requirements without affecting other requirements • Ex:Fridge door – Req » Access to food » Minimal energy loss – Vertical door » Access to food » No Minimal energy loss – Horizontal door » Provides both requiremnt• Axiom 2 – Minimize the information content of the design
  • 5. corollary• Called design rules• Derived from axioms
  • 6. corollaries• Corollary 1 – Uncoupled design with less information content• Corollary 2 – Single purpose• Corollary 3 – Large number of single classes• Corollary 4 – Strong mapping• Corollary 5 – standardization• Corollary 6 – Design with inheritance
  • 7. Corollary 4 Corollary 1 Axiom1 Corollary 2 Axiom2 Corollary 3Corollary 5 Corollary 6
  • 8. Corollary 1• Uncoupled design with less information content – Goal • Maximize cohesiveness • Improve coupling • Less information transaction among objects – Coupling • Deals interaction among objects – Types of coupling • Interaction coupling – Involves the amount and complexity of messages bw components – Tightly coupled objects leads to change in one object reflects changes in others • Inheritance coupling – Inheritance is form of coupling bw super and sub class – High Inheritance coupling is desirable – Cohesion • Deals interaction within a single objects • Reflects single purpose ness • High cohesiveness can lower coupling
  • 9. Corollary 2• Single purpose – Each class must have a purpose – Clearly defined and necessary in the context of achieving system’s goals
  • 10. Corollary 3• Large number of single classes, reusability – The less specialized the classes are, the more likely future problems can be solved by a recombination of existing classes – Smaller classes • less specialized • Chance of reusing – Large and complex classes • More specialized • Less chances of reusing
  • 11. Corollary 4• Strong mapping – As the model progress from analysis to implementation, more detail is added, but it remains the same – Strong mapping links classes identified during analysis and design phase
  • 12. Corollary 5• Standardization – Documentation • Knowledge of existing classes helps to identify new classes
  • 13. Corollary 6• Design with inheritance

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