1. Software Design Principles

2. Software Design Principles 1
Being presented by
Mr. Ritesh Singh

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

4. 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

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

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

7. 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

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

9. 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

10. System Models 10
Types of System Model
Process
Data-processing
Classification
Composition
Stimulus-response

11. System Models :: Composition Model 11
Data-flow ModelsTypes of System Model
Process
Data-processing
Classification
Composition
Stimulus-response

12. 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

13. System Models 13
Types of System Model
Process
Data-processing
Classification
Composition
Stimulus-response

14. System Models :: Classification Model 14
Data-flow ModelsTypes of System Model
Process
Data-processing
Classification
Composition
Stimulus-response

15. 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

16. 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

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

18. Software Design:: Activities 18
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

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

20. Software Design:: Activities 20
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

21. Software Design 21
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

22. 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

23. Software Design :: Process 23
Design Activities (Actions):
Architectural
Design
1
Abstract
Specification
2

24. Software Design :: Process 24
Interface
Design
3
Component
Specification
4

25. Software Design :: Process 25
Data
Structure
Design5
Algorithm
Design
6

26. Software Design :: Process 26
Sub-systems making up the system and
their relationships
Architectural
Design
1

27. Software Design :: Process 27
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

28. Software Design :: Process 28
Developing a method for two (or more) modules
in a system to connect and communicate
Interface
Design
3

29. Software Design :: Process 29
Services are allocated to different components and
the interfaces of these components are designed.
Component
Design
4

30. Software Design :: Process 30
The data structures used in the system
implementation is designed in detail and specified.
Data
Structure
Design5
*Data Structure : storing and organizing data

31. Software Design :: Process 31
A specific method to create a mathematical process
in solving problems.
Algorithm
Design
6
*Algorithm : step-by-step procedure for calculations

32. Software Design:: Activities 32
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

33. Software Design 33
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

34. 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.

35. Software Design:: Activities 35
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

36. Software Design 36
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

37. 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

38. 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..

39. Software Design:: Activities 39
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

40. Software Design 40
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

41. 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

42. Software Design:: Activities 42
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

43. Software Design 43
ProcessProcess
MethodsMethods
DescriptionDescription
StrategiesStrategies
QualityQuality

44. 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

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

46. Architectural Design 46
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

47. Architectural Design :: System Structuring 47
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

48. Architectural Design :: System Structuring 48
• 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

49. Architectural Design :: System Structuring 49
System structuring
Repository model
 Client-server model
 Abstract machine 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

50. Architectural Design :: System Structuring 50
System structuring
 Repository model
Client-server model
 Abstract machine 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

51. Architectural Design :: System Structuring 51
System structuring
 Repository model
 Client-server model
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

52. Architectural Design 52
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

53. Architectural Design :: Control Models 53
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

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

55. Architectural Design ::Control models 55
Control models
Centralized control Event-based Control
• One sub-system designated as the system controller
System
Controller
Computation
Process
Sensor
Processes
Actuator
Processes
Fault
Handler
Laser
Interface

56. Architectural Design ::Control models 56
Control models
Centralized control Event-based Control
• 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

57. Architectural Design 57
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

58. Architectural Design :: Control Models 58
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

59. 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

60. Architectural Design 60
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

61. Architectural Design :: Control Models 61
System Structuring
Control models
Modular decomposition
Domain-specific architectures
Activities Involves

62. 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

63. Summary 63
 System Models
 Software Design
 Architecture Design

64. Thank you for your time. 
1