Unit 4 discusses object oriented design processes and axioms. The key points are: 1. The object oriented design process involves defining classes, methods, attributes and associations, applying design axioms to refine UML diagrams, and testing design through prototypes and use cases. 2. There are two main axioms - maintaining independence of components and minimizing information content. 3. Corollaries derived from the axioms include uncoupled design with less information, single purpose classes, large number of small reusable classes, strong mapping from analysis to implementation, standardization, and inheritance-based design.

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