Software design principles

Software Design Principles 1
Being presented by
Mr. Ritesh Singh

Thanks. 1
Special thanks to Ms. Charu Jain for this initiave

Introduction 4
Software: A set of programs which helps user to execute
its task using the system
Design: creation of a plan to construct a system
Principles: Rules or laws to be followed
Demystifying the subjectDemystifying the subject

Objectives 5
• Clearly understand the software design
principles
• Follow the structured approach for the software
design
• Understand different models

System Models 6
System : A collection of components placed together to perform a task which
is beyond components’ individual capability.

System Models 7
Types of System Model
Process
Data-processing
Classification
Composition
Stimulus-response
• data flow diagram
• entity relation diagram
• object class/inheritance diagram
• State transition diagram
• Used to show the principal
activities

System Models :: Data processing Model 8
Data-flow ModelsTypes of System Model
Process
Data-processing
Classification
Composition
Stimulus-response

System Models :: Data-flow Models 9
• Used to model the way data is processed in the system
• Notation Used:
Rounded corner rectangle -> Processing steps
Rectangle -> Data Stores
Arrows -> Flow of data

System Models 10
Process
Data-processing
Classification
Composition
Stimulus-response

System Models :: Composition Model 11
Process
Data-processing
Classification
Composition
Stimulus-response

System Models :: Semantic-data Model 12
• Semantics of data
• Identifies entity in a database, their attributes
and explicit relationship b/w them
Notation Used:
<Nam
e>
<name>
An entity
Input Cardinality
Output Cardinality
<name> An entity or
Relation attribute

System Models 13
Process
Data-processing
Classification
Composition
Stimulus-response

System Models :: Classification Model 14
Process
Data-processing
Classification
Composition
Stimulus-response

System Models :: Object Model 15
• Represent both data and its processing
• Combination of some of uses of DFD and SDM
Notation Used:
<class name>
<Attribute>
<Service>
Object Class

System Models :: Data Dictionaries 16
• List of name used by the systems, arranged alphabetically.
Advantage:
 mechanism for name management
 store of organization information which can link analysis, design,
implementation, and evaluation
Names* -> entities, types, relations, attributes or services

Software Design 17
What is software design?
"all the activities involved in conceptualizing,
framing, implementing, commissioning, and
ultimately modifying complex systems“
-Wikipedia

Software Design:: Activities 18
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

Software Design 19
To put it simply:
"the activity following requirements specification
and before programming."
Design
Requirement
Specification Programming

ProcessProcess
MethodsMethods
QualityQuality

Software Design 21
ProcessProcess
MethodsMethods
QualityQuality

Software Design :: Process 22
What is a process?
A series of actions or steps taken to
achieve an end.
Action 1 Action 2 Action 3 Action 4 Action nPROCESS

Design Activities (Actions):
Architectural
Design
1
Abstract
Specification
2

Interface
Design
3
Component
Specification
4

Data
Structure
Design5
Algorithm
Design
6

Sub-systems making up the system and
their relationships
Architectural
Design
1

For each sub-system, an abstract specification of
the services it provides and the constraints
under which it must operate is produced.
Abstract
Specification
2

Developing a method for two (or more) modules
in a system to connect and communicate
Interface
Design
3

Services are allocated to different components and
the interfaces of these components are designed.
Component
Design
4

The data structures used in the system
implementation is designed in detail and specified.
Data
Structure
Design5
*Data Structure : storing and organizing data

A specific method to create a mathematical process
in solving problems.
Algorithm
Design
6
*Algorithm : step-by-step procedure for calculations

ProcessProcess
MethodsMethods
QualityQuality

Software Design 33
ProcessProcess
MethodsMethods
QualityQuality

Software Design :: Methods 34
1. Data flow model: data transformations
2. Entity relation model: logical data structures being used
3. Structural model: System components and their interactions
are documented
4. Object oriented model: a model of how objects are
composed of other objects and, usually, an object use
model which shows how objects are used by other objects.

ProcessProcess
MethodsMethods
QualityQuality

Software Design 36
ProcessProcess
MethodsMethods
QualityQuality

Software Design :: Description 37
Role:
•Basis for detailed implementation
•communication medium between designers of sub-systems
•Info to system maintainers about the original intentions of the system designers
Notations Used:
Graphical notations
Program description languages
Informal text

Software Design :: Description 38
1. Graphical notations:
• Display the relationships between the components making up the design
and to relate the design to the real-world system.
• Most useful for giving an overall picture of the system.
2. Program description languages:
• use control and structuring constructs based on programming language
constructs but also allow explanatory text and additional types of
statement to be used.
• intention of the designer is expressed rather than the details of how the
design is to be implemented.
3. Informal text:
1. Information about design rationale or non-functional considerations may
be expressed using natural language text.
Continue..

ProcessProcess
MethodsMethods
QualityQuality

Software Design 40
ProcessProcess
MethodsMethods
QualityQuality

Software Design :: Strategies 41
1. Functional design:
• functional viewpoint, starting with a high-level view and progressively
refining this into a more detailed design.
• Example: Jackson Structured Programming and the Warnier-Orr method
2. Object oriented design:
• system is viewed as a collection of objects rather than as functions.
• JSD is a design method that falls somewhere between function oriented
and object oriented design.
*JSD : Jackson System Develpment

ProcessProcess
MethodsMethods
QualityQuality

Software Design 43
ProcessProcess
MethodsMethods
QualityQuality

Software Design :: Quality 44
• The design components should be cohesive
• Loosely coupled
Coupling the independence of components.
• looser the coupling, easier it is to adapt the design.
Good Design Efficient code

Architectural Design 45
What is a it?
Initial design process of identifying sub-system
and establishing a framework for sub-system
control and communication

System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

Architectural Design :: System Structuring 47
System Structuring
Control models
Activities Involves

• Decompose a system into a set of interacting sub-systems
• Notations Used:
• Box -> Sub system
• Boxes within boxes -> sub-system has been decomposed to
sub-systems
• Arrow -> direction of data and/or control
System structuring
 Repository model
 Client-server model
 Abstract machine model

System structuring
Repository model
• Data is held in a central database
• Accessed by all sub-systems
Project repository
Design
editor
Code
Generator
Design
analyzer
Report
Generator
Program
editor
Design
translator

System structuring
Client-server model
• Distributed sys model
• Standalone servers offer service to sub-sys (clients)
• A network
Network
Catalog
server
Video
server
Client 1
Picture
server
Hypertext
server
Client 2 Client 4Client 3

System structuring
Abstract machine model
• Layered
• Layers provide a set of service to layer above
• Supports incremental development
• Changeable and portable
Client 2Client 2Operating system
Database Management
Object Management
Version Management

System Structuring
Control models
Activities Involves

Architectural Design :: Control Models 53
System Structuring
Control models
Activities Involves

Architectural Design ::Control models 54
• Control flow b/w sub-system
Control models
Centralized control Event-based Control

Control models
• One sub-system designated as the system controller
System
Controller
Computation
Process
Sensor
Processes
Actuator
Processes
Fault
Handler
Laser
Interface

Control models
• Driven by externally generated events
Broadcast models Interrupt-driven models
• Broadcast to all, but particular
sub-system responds to it
• Used in Real time sys
• Interrupt handler

System Structuring
Control models
Activities Involves

Architectural Design ::Modular Decomposition 59
Modular Decomposition
Object-oriented design Data-flow models
• Sys is decomposed into
a set of communicating objects
• Sys is decomposed into
functional modules
• Also called Pipeline Approach

System Structuring
Control models
Activities Involves

Architectural Design :: Domain-specific architecture 62
Domain-specific Architecture
Generic models Reference models
• Abstraction of many
real systems
• contains Principal characteristics
• Describe a larger class of systems
• Informs Sys Architect about that
Class of sys
Generic models Vs. Reference models
Derived from “bottom-up”
from existing system
Derived from “top-down”
from existing system

Summary 63
 System Models
 Software Design
 Architecture Design

Thank you for your time. 
1

Software design principles

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