Fundamental design concepts

Submitted By,
M. Lavanya, M.Sc.(CS&IT),
P. Nithya, M.Sc.(CS&IT),
N. Pandimeena, M.Sc.(CS&IT),
Nadar Saraswathi College of Arts & Science, Theni.
FUNDAMENTAL DESIGN CONCEPTS

Fundamental concepts of software design
includes the following techniques,
1. Abstraction
2. Structure
3. Information Hiding
4. Modularity
5. Concurrency
6. Verification
7. Design Aesthetics

Abstraction is the intellectual tool that allows us to deal
with concepts apart from particular instances of those
concepts.
Three widely used abstraction mechanisms in software
design are,
1. Functional Abstraction
2. Data Abstraction
3. Control Abstraction
These mechanisms allow us to control the complexity
of the design process by systematically proceeding from the
abstract to the concrete.
ABSTRACTION

Information hiding is a fundamental design concept for
software. Each module in the system hides the internal details
of its processing activities and modules communicate only
through well-defined interfaces.
Other candidates for information hiding include:
1. A data structure and its internal linkage
2. The format of control blocks such as those for
queues in an operating system
3. Character codes
4.Shifting, masking and other machine
dependent details
INFORMATION HIDING

Structure is a fundamental characteristic of computer
software.
The use of structuring permits decomposition of a large
system into smaller, more manageable units with well-defined
relationships to the other units in the system.
The most general form of system structure is the network.
Software System Structure
Network
STRUCTURE
Link
Node

Node
The nodes can represent processing elements that
transform data and the arcs can be used to represent data links
between nodes.
Alternatively, the nodes can represent data stores and
the arcs data transformation.
Environment group templates
Shared objects
Processes

Process
Each process, one might find functional abstraction
groups, data abstraction groups, and control abstraction groups.
Template group
Processing groups
Utility group

Group
Each group might consist of a visible specification part
and a hidden body.
The visible portion would provide attributes such as
procedure interfaces, data types, and data objects available for
use by other groups.
Visible part
Static area
Hidden part

The term of “module” a module is FORTRAN sub routine
 module ada package "to” module is a work of individual
programmer
Modular system is collection of abstraction
• Data abstraction
• Function abstraction
• Control abstraction
 The abstraction to handle problem to solved
 Modularity enhance design clarity
• Implementation
• Debugging
• Testing
• Document
• Maintenance
MODULARITY

Modular system include:
i) Well defined sub system
ii) Each abstraction single
iii) More than one major structure
iv) Function share global data
v) Function abstract data type

 Software system can be categorized as
Sequential
Concurrency
 Sequence system can activate at any time.
 Concurrency system can process simutanuously using
multiprocess available.
 The implementation of time sharing, multiprocessor, real
time system and Concurrency system include:
Deadlock
Mutual exclusion
Synchronization
CONCURRENCY

DEADLOCK
 When process in computer system are waiting are other
process executed
MUTUAL EXCLUSION
 Mutual exclusion multi process do not attempt ,same
component at share process at a time
SYNCHRONIZATION
 Concurrent process at different execution speed
CONCURRENCY PRINCIPLE
 Fundamental of software design

Verification is a fundamental concept in
software design.
The verification technique has two steps:
i) verification is software requirement
definition satisfied customer need
ii) verification is the design satisfied
requirement definition
VERIFICATION

Aesthetics is fundamental to design, whether in art
or technology.
• Simplicity,
• Clarity,
• Elegance
• Quality of product
The mathematical elegance or structure beauty the
properties of satisfaction of requirements
AESTHETICS

MODULES AND
MODULARIZATION CRITERIA

CHARACTERISTICS
A software module to be a named entity
having the following characteristics:
 Modules contain instructions, processing logic, and
data structures.
 Modules can be separately compiled and stored in a
library.
 Modules can be included in a program.
 Module segments can be used by invoking a name
and some parameters.
 Modules can use other modules.

EXAMPLES
 Examples of modules include procedures,
subroutines, and functions; functional groups of
related procedures, subroutines, and functions;
data abstraction groups; utility groups and
concurrent processes.
 Modularization allows the designer to
decompose a system into functional units, to
impose hierarchical ordering on function usage,
to implement data abstractions, and to develop
independently useful subsystems.

COUPLING AND COHESION
Coupling:
The strength of coupling between two modules is
influenced by the complexity of the interface, the type of
connection, and the type of communication.
Coupling between modules can be ranked on a scale of
strongest(least desirable) to weakest(most desirable) as
follows:
Content coupling
Common coupling
Control coupling
Stamp coupling
Data coupling

Content Coupling:
Content coupling occurs when one module
modifies local data values or instructions in
another module.
Common Coupling:
Modules are bound together by global data
structures.
Control Coupling:
Control coupling involves passing control
flags(as parameters or globals) between modules
so that one module controls the sequence of
processing steps in another module.

Stamp Coupling:
Stamp coupling is similar to common
coupling, except that global data items are shared
selectively among routines that require the data.
Data Coupling:
Data coupling involves the use of parameter
lists to pass data items between routines.
The most desirable form of coupling between
modules is a combination of stamp and data
coupling.

Cohesion:
The internal cohesion of a module is measured in
terms of the strength of binding of elements within the
module.
Cohesion of elements occurs on the scale of
weakest(least desirable) to strongest(most desirable) in
the following order:
Coincidental cohesion
Logical cohesion
Temporal cohesion
Communication cohesion
Sequential cohesion
Functional cohesion
Informational cohesion

Coincidental Cohesion:
Coincidental cohesion occurs when the
elements within a module have no apparent
relationship to one another.
Logical Cohesion:
Logical cohesion implies some relationship
among the elements of the module.
Ex: In a module that performs all input and
output operations, or in a module that edits all data.

Temporal Cohesion:
Modules with temporal cohesion exhibit
many of the same disadvantages as logically
bound modules.
A typical example of temporal cohesion is a
module that performs program initialization.
Communication Cohesion:
The elements of a module possessing
communicational cohesion refer to the same set of
input and/or output data.
Ex: “Print and Punch the Output File” is
communicationally bound.

Sequential Cohesion:
Sequential cohesion of elements occurs when the
output of one element is the input for the next element.
Functional Cohesion:
Functional cohesion is a strong, and hence
desirable, type of binding of elements in a module
because all elements are related to the performance of
a single function.
Informational Cohesion:
Informational cohesion of elements in a module
occurs when the module contains a complex data
structure and several routines to manipulate the data
structure.

OTHER MODULARIZATION
CRITERIA
Additional criteria for deciding which functions
to place in which modules of a software system
include:
Hiding difficult and changeable design decisions
Limiting the physical size of modules
Structuring the system to improve observability and
testability
Isolating machine dependencies to a few routines
Easing likely changes
Providing general purpose utility functions
Reducing the call return overhead of excessive subroutine
calls.

Fundamental design concepts

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