1. Software Design

2. Software design
Deals with transforming the customer requirements, as described in the SRS document, into a form that is implementable using a programming language
The following items must be designed during design phase:
Different modules required to implement the design solution
Control relationship among the identified modules
Interface among different modules
Data structures of the individual modules
Algorithms required to implement the individual modules

3. Two design activities Preliminary (or high level) design
Identification of different modules, the control relationships and the definitions of the interfaces among them
Outcome of this activity is called program structure or s/w architecture
Structure chart
Detailed design
The data structure and algorithms of the different modules are designed
Outcome of the detailed design stage is known as module specification document

4. How to distinguish a good s/w design from a bad one?
Goodness is dependent on the targeted application
The notion of good design varies
Desirable characteristics:
Correctness
Understandability
Efficiency
maintainablility

5. Modularity Decomposition of a problem into modules facilitates design
If different modules are independent of each other, then each module can be understood separately
Reduces complexity of the design solution
Modules should be cleanly decomposed
They should be arranged in a neat hierarchy

6. Clean decomposition
Modules should display high cohesion and low coupling
Modules are more or less independent of each other

7. Neat arrangement Characterized by: Layered solution Low fan-out and
Abstraction

8. Cohesion & Coupling
Primary characteristics of a neat module decomposition are high cohesion and low coupling- then it is functionally independent of other modules
Cohesion: measure of the functional strength of a module
Coupling between two modules: measure of the degree of interdependence or interaction between them

9. Functional independence
A module having high cohesion and low coupling is said to be functionally independent of other modules
Functional independence means that a cohesive module performs a single task or function
A functionally independent module has minimal interaction with other modules.

10. Functional independence
FI is key to any good design due to:
Error isolation
Scope for reuse
Understandability