Page 148 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes 3. ........................ is the first design state for devising the basic approach to solving the problem.
4. The system architecture determines the organization of the system into ........................

12.2 System Design Decisions

During system design, the design decisions that are to be made are discussed in the unit.

12.2.1 Reuse Plan

Reuse is often cited as an advantage of OO technology. But reuse does not happen automatically.
There are two different aspects – using existing things and creating reusable new things. It is
much easier to use existing things than to design new things for uncertain use to come. Reusable
things include models, libraries, frameworks and patterns. Reuse of models is often the post
practical form of reuse. The logic in a model can apply to multiple problems.

A Library is a collection of classes that are useful in many contexts.

!
Caution The collection of classes must be carefully organized, so that users can find them.
There must be several qualities for a good library:
1. Coherence

2. Completeness
3. Consistency
4. Efficiency
5. Extensibility

6. Generality
7. Problems related with libraries
8. Argument validation
9. Error handling

10. Control paradigms
11. Group operations
12. Garbage collection
13. Name collisions

Frameworks based Reuse

A frame work is skeletal structure of a program that must be elaborated to build a complete
application. This elaboration often consists of specializing abstract classes with behavior specific
to an individual application. A class library may accompany a frame work.

Pattern based Reuse

A pattern is a proven solution to general problem. Various patterns target different phases of
the software development life cycle. There are patterns for analysis, architecture, design and
implementation. A pattern is different from framework. A pattern is typically a small number

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