1. Unit 4
Object 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 on
associations 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 3
Corollary 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