1. Software Design Lecture : 6

2. Software Design Components
Principle
Criteria
Techniques

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4. Myth about Abstraction
Problem Statement
Our task is to design an management information system for a hospital, it should include patient management, doctors management , laboratory management , inventory of equipment and medicines,

5. Traditional Approach Programmers Approach:
‘Which Technology to use for implementation ‘
System Architect Approach
Forget the technology, first understand what to do in detail , generate Requirement Specification (RS)– This is Abstraction ,

6. Abstraction What to Do not How to do !!
A view of an object that focuses on the information relevant to a particular purpose and ignores the remainder of the information.
IEEE Standard
Abstraction is generally used for handling and
reducing complexity
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7. Abstraction continue...
Abstraction is simply removal of unnecessary details.
To design a complex system, you must identify what about that part other parts should know in order to design their part ,

8. Benefits of Abstraction
Gives the designer freedom to ignore certain details, for the time being, and to determine or design the "big picture" aspects of his design

9. Decomposition Splitting one system into smaller components
Designing the components independently.
For the outside world the components are reduced to their interfaces
“Divide and Conquer”
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10. Decomposition Rules Don't design components to correspond to execution
steps – look for similar tasks – No Run-time binding
Decompose so that all design decision have a
minimum effect to the rest of the system – anything
that soaks the system will be expensive to change ,

11. Decomposition continues....
Components should be specified by all information needed to use the component – nothing less and nothing more!

12. Subsystems
A Subsystem is a secondary or subordinate system within a system. IEEE Standard

13. Subsystems
A subsystem is a functionally cohesive grouping of classes that is a major part of a larger aggregate system
Can be independently ordered, configured or delivered
Subsystems are related to each other via dependency relations, and communicate with each other via well- defined interfaces
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14. Subsystems
Decompose by functional services i-e Database Subsystem, User Interface Subsystem etc

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16. Subsystem Example Student Management Accounts Library Management
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Library Management
Hrm and Payroll

17. Layers Decomposition of the system into smaller, more
manageable units, that are layered hierarchically.
Each layer supplies one level of abstraction
A layer only uses services of the next underlying
layer
Layers can be tested independently
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20. Layers Rule
Layer can request for services from exactly one layer below it.
Layer can respond to a request of a layer exactly one layer above it.
Total Layers = N = 3
Request = N-1
Response = N+ 1
Example on next slide
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21. Layer Rule High Level Architectural Diagram
Services Layers
Request
Operations Layers
Response
Student Data Management