Software Design
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Lecter notes which is cover in class, Lecture notes of Software Engineering
Lecter notes which is cover in class and for exam prepration
Typology: Lecture notes
2021/2022
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Software Design
Introduction
Design phase transforms SRS
document:
into a form easily implementable in
some programming language.
SRS Document
Design Activities
Design Documents
Module Structure
Introduction
A module consists of:
1. several functions
2. associated data structures.
Data
Functions
D ..
D ..
D ..
F ..
F ..
F ..
F ..
F ..
Introduction
Design activities are usually
classified into two stages:
- preliminary (or high-level) design
- detailed design.
High-level design
Identify:
- modules
- control relationships among modules
- interfaces among modules.
d1 d
d d
d
HIGH LEVEL DESIGN
- (^) Several Notations available to
represent high level design:
Usually a tree like structure called
STRUCTURE CHART is used
Detailed design
For each module, design:
1. data structure
2. algorithms
Outcome of detailed design:
module specification.
Good and Bad Designs
- (^) There is no unique way to design a
system’
- (^) Even using the same design
methodology:
- (^) Different designers arrive at
different design solutions
- (^) We need to distinguish between
good and bad designs.
Which of two is a better
design:
- (^) Should implement all the
functionalities of system correctly’
- (^) Should be easy understandable’
- (^) Should be efficient
- (^) Should be easily amenable to
change
- (^) i.e. easy maintainable
How are abstraction and
Decomposition principles
used in designs?
- (^) Two Ways:
Modular Design
Layered Design
What Is Good Software
Design?
Unless a design is easy to understand,
tremendous effort needed to maintain it.
We already know that about 60% effort
is spent in maintenance.
If the software is not easy to
understand:
maintenance effort would increase
many times.
Modularity
Modularity is a fundamental
attributes of any good design.
Decomposition of a problem cleanly
into modules:
- Modules are almost independent
of each other
- divide and conquer principle.
Modularity
If modules are independent:
modules can be understood
separately.
reduces the complexity greatly.
To understand why this is so,
remember that it is very difficult to break
a bunch of sticks but very easy to break
the sticks individually.