This document discusses key concepts in software design. It covers the software design process, principles of good design including modularity, abstraction, and refinement. It also discusses design concepts such as cohesion, coupling, and software architecture. The document was prepared by Dr. T. Thendral and provides an overview of important topics for software engineers to consider when designing software systems.

1. SOFTWARE DESIGN
Prepared by Dr.T.Thendral 15.07.23
Prepared by
Dr.T.Thendral
Assistant Professor
Department of Computer Science
Sri Ramaskrishna College of Arts & Science for Women
Coimbatore

2. • Software design and Software engineering
• The Design process
• Design principles
• Design concepts
• Effective modular design
• Software Architecture
Prepared by Dr.T.Thendral 15.07.23

3. SOFTWARE DESIGN AND SOFTWARE
ENGINEERING
• Software design is the first of
three technical activities—
design, code generation, and
test—that are required to
build and verify the software
• The design task produces a
data design, an architectural
design, an interface design,
and a component design
• The data design transforms
the information domain model
created during analysis into
the data structures that will be
required to implement the
software
Prepared by Dr.T.Thendral 15.07.23

4. • The architectural design defines the relationship
between major structural elements of the software,
the “design patterns”
• The interface design describes how the software
communicates within itself, with systems that
interoperate with it and with humans who use it
• An interface implies a flow of information (e.g., data
and/or control) and a specific type of behavior
• The component-level design transforms structural
elements of the software architecture into a
procedural description of software components
Prepared by Dr.T.Thendral 15.07.23

5. • The importance of software design can be
stated with a single word—quality
• Design is the place where quality is fostered in
software engineering
Prepared by Dr.T.Thendral 15.07.23

6. Translating the analysis model into
a software design
Prepared by Dr.T.Thendral 15.07.23

7. THE DESIGN PROCESS
• Software design is an iterative process
through which requirements are translated
into a “blueprint” for constructing the
software
Prepared by Dr.T.Thendral 15.07.23

8. Design and Software Quality
• Throughout the design process, the quality of
the evolving design is assessed with a series of
formal technical reviews or design
walkthroughs
Prepared by Dr.T.Thendral 15.07.23

9. Three characteristics of a good design:
Prepared by Dr.T.Thendral 15.07.23

10. • A design should exhibit an architectural
structure that
• (1) has been created using recognizable design
patterns
• (2) is composed of components that exhibit
good design characteristics, and
• (3) can be implemented in an evolutionary
fashion, thereby facilitating implementation
and testing
Prepared by Dr.T.Thendral 15.07.23

11. • 2. A design should be modular
• 3. A design should contain distinct representations of data,
architecture, interfaces, and components (modules).
• 4. A design should lead to data structures that are
appropriate for the objects
• 5. A design should lead to components that exhibit
independent functional characteristics
• 6. A design should lead to interfaces that reduce the
complexity of connections between modules and with the
external environment
• 7. A design should be derived using a repeatable method
that is driven by information obtained during software
requirements analysis
Prepared by Dr.T.Thendral 15.07.23

12. The Evolution of Software Design
• Early design work concentrated on criteria for the
development of modular programs and methods
for refining software structures in a top-down
manner
• Procedural aspects of design definition evolved
into a philosophy called structured programming
• Later work proposed methods for the translation
of data flow or data structure into a design
definition
Prepared by Dr.T.Thendral 15.07.23

13. • Methods have a number of common
characteristics:
• (1) a mechanism for the translation of analysis
model into a design representation
• (2) a notation for representing functional
components and their interfaces
• (3) heuristics for refinement and partitioning, and
• (4) guidelines for quality assessment
Prepared by Dr.T.Thendral 15.07.23

14. Example
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DESIGN PRINCIPLES

15. DESIGN PRINCIPLES
• Software design is both a process and a model
• Design should be Creative skill, past
experience, a sense of what makes “good”
software, and an overall commitment to
quality are critical success factors for a
competent design
• The design model is the equivalent of an
architect’s plans for a house
Prepared by Dr.T.Thendral 15.07.23

16. • e.g., a three-dimensional rendering of the
house
• slowly refines the thing to provide guidance
for constructing each detail (e.g., the
plumbing layout)
Prepared by Dr.T.Thendral 15.07.23

17. • The design process should not suffer from
“tunnel vision.”- onsider alternative
approaches
• The design should be traceable to the
analysis model- Because a single element of
the design model often traces to multiple
requirements
• Requirements have been satisfied by the
design model!
Prepared by Dr.T.Thendral 15.07.23

18. • The design should not reinvent the wheel-
Systems are constructed using a set of design
patterns
• These patterns should always be chosen as an
alternative to reinvention
• Time is short and resources are limited
• The design should “minimize the intellectual
distance” between the software and the
problem as it exists in the real world.
• structure of the software design should mimic
the structure of the problem domain
Prepared by Dr.T.Thendral 15.07.23

19. • The design should exhibit uniformity and
integration-
• A design is uniform if it appears that one
person developed the entire thing.
• Rules of style and format should be defined
for a design team before design work begins
• design is integrated if care is taken in defining
interfaces between design components
Prepared by Dr.T.Thendral 15.07.23

20. • The design should be structured to accommodate
change
• The design should be structured to degrade
gently, even when a’berrant data, events, or
operating conditions are encountered
• Design is not coding, coding is not design
• The design should be assessed for quality as it is
being created, not after the fact
• The design should be reviewed to minimize
conceptual (semantic) errors
Prepared by Dr.T.Thendral 15.07.23

21. Prepared by Dr.T.Thendral 15.07.23

22. DESIGN CONCEPTS
• Each helps the software engineer to answer
the following questions:
• What criteria can be used to partition
software into individual components?
• How is function or data structure detail
separated from a conceptual representation of
the software?
• What uniform criteria define the technical
quality of a software design?
Prepared by Dr.T.Thendral 15.07.23

23. • The beginning of wisdom for a [software
engineer] is to recognize the difference
between getting a program to work, and
getting it right“
• Fundamental software design concepts
provide the necessary framework for "getting
it right"
Prepared by Dr.T.Thendral 15.07.23

24. Abstraction
• Abstraction:
• When we consider a modular solution to any problem,
many levels of abstraction can be posed
• Procedural Abstraction
• An example of a procedural abstraction would be the word
open for a door
• Data abstraction
• A data abstraction is a named collection of data that
describes a data object
• In the context of the procedural abstraction open, we can
define a data abstraction called door
• data object, the data abstraction for door (e.g., door type,
swing direction, opening mechanism, weight, dimensions)
Prepared by Dr.T.Thendral 15.07.23

25. • Control abstraction is the third form of
abstraction used in software design
• control abstraction implies a program control
mechanism without specifying internal details
Prepared by Dr.T.Thendral 15.07.23

26. EFFECTIVE MODULAR DESIGN
• The concept of functional independence is a
direct outgrowth of modularity and the concepts
of abstraction and information hiding
• Independence is measured using two qualitative
criteria: cohesion and coupling.
• Cohesion is a measure of the relative functional
strength of a module.
• Coupling is a measure of the relative
interdependence among modules
Prepared by Dr.T.Thendral 15.07.23

27. Refinement
• Stepwise refinement is a top-down design
strategy originally proposed by Niklaus Wirth
• In each step (of the refinement), one or several
instructions of the given program are
decomposed into more detailed instructions
• Refinement is actually a process of elaboration
• Abstraction enables a designer to specify
procedure and data and yet suppress low-level
details
• Refinement helps the designer to reveal low-level
details as design progresses
Prepared by Dr.T.Thendral 15.07.23

28. Modularity
• software is divided into separately named and
addressable components, often called
modules, that are integrated to satisfy
problem requirements
Prepared by Dr.T.Thendral 15.07.23

29. Prepared by Dr.T.Thendral 15.07.23

30. • Modular decomposability - reduce the complexity of the
overall problem, thereby achieving an effective modular
solution
• Modular composability-If a design method enables existing
(reusable) design components to be assembled into a new
system
• Modular understandability-If a module can be understood
it will be easier to build and easier to change
• Modular continuity-If small changes to the system
requirements result in changes to individual modules
• Modular protection-If an aberrant condition occurs within
a module and its effects are constrained within that module
side effects will be minimized.
Prepared by Dr.T.Thendral 15.07.23

31. Software Architecture
• Software architecture the overall structure of
the software and the ways in which that
structure provides conceptual integrity for a
system
• One goal of software design is to derive an
architectural rendering of a system
• A set of architectural patterns enable a
software engineer to reuse designlevel
concepts
Prepared by Dr.T.Thendral 15.07.23