System Design

Design Objectives: System design is to deliver the requirements as specified in the feasibility report. The main objectives of the design are

1. Practicality
2. Efficiency
3. Cost
4. Flexibility
5. Security

System design contains Logical Design & Physical Designing, logical designing describes the structure & characteristics or features, like output, input, files, database & procedures. The physical design, which follows the logical design, actual software & a working system. There will be constraints like Hardware, Software, Cost, Time & Interfaces.

The processing techniques are

Ø Batch Processing
Ø Real-time
Ø Online
Ø Combination of all

Structured design is a data flow methodology. The graphical representation of data flow, communication & defining the modules & their relationship with each is known as Structure Chart. This method decomposes & modularizes the system so that the complexity & manageability will come down. Thus reducing the intuitive reasoning & promotes the maintainable provable systems.

This type of design follows top-down & hierarchy, which will have one single entry & single exit, The advantages of this method are

1. Critical interfaces are tested first
2. Early versions of the design, through incomplete are useful enough to resemble the real system
3. Structuring provides control & improve morale
4. The procedural characteristics define the order that determines processing.

Major System Design Activities are

1. DB design
2. Program design
3. System & program test preparation
4. System Interface Specification
5. Audit Consideration
6. Audit control & Documentation control

Major design process parts are

1. O/p design
2. I/p design
3. File Design
4. Procedure design
- Computer design
- Non-computer design
5. Control design

These parts are inter-dependent on each other. System Specifications is a document, which will have a result of system design process, it serves as a Blue print for the project development & maintenance.

Prototype is a working system that is developed to test ideas & assumptions about a new system.

Objectives of Input Design are

1. Controlling amount of I/p
2. Avoiding delay
3. Avoiding errors in data
4. Avoiding extra steps
5. Keeping the process simple.

Major concerns about the input

1. What input is needed
2. How & where is i/p is created
3. How should source documents designed
4. What format should be used for Input
5. What medium should be used to store data

Input Verification can be done using

Key verification
Use of self checking numbers
Visual display

Hash Total
Checking between range
Reasonableness Test

Verification of Codes
Verification of data Type
Verify Combination data

Sequence Check

Concerns for designing a CRT i/p screen

1. Easy to use
2. Improved processing speed
3. Menu driven Approach
4. Highlighting the information on screen
5. Usage of appropriate colors
6. Editing thru display screens

Types of Outputs are

1. Application o/p
2. Operating O/p

Output devices are

1. VDU
2. Printer
3. Computer output Microfilm (COM)

Output Design Consideration are done using following points

Type of user & purpose
Content
Format

Frequency & times
Volume
Sequence

Quality
Type of stationary

Points to be considered while designing a Menu

1. Hierarchical
2. Termination
3. Skipping Menu
4. Security Control

Types of Forms

1. Action
2. Memory
3. Report

Computer Graphics are of three types

1. Presentation graphics
2. Decision support Graphics
3. Graphics Hardware/software.

Different types of files are

Master
Transaction
Backup

Archive
Table
Report

Dump
Library

File organizations are

1. Sequential/Relational
2. Random
3. Indexed

Major criteria for selecting a File organization are

1. Method of processing of file
2. Size of data
3. File inquiry capability
4. File volatility
5. Response time
6. Activity ratio

A database is a set of logically related files organized to facilitate access by one or more applications programs & to minimize data redundancy. Main objectives of DB are

1. Eliminate the redundancy of data
2. Data integrity
3. Share data among users
4. Incorporate changes quickly & easily
5. Simplify the use of data
6. Cost effective
7. Improve accuracy & consistency
8. Exercise central control over standards

To manipulate the operations on the DB, a set of programs are maintained called Data Base management System (DBMS). The Main advantages of DB are

1. File consolidation
2. Program & file independence
3. Access versatility
4. Data Security
5. Program development
6. Program maintenance
7. Special information

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