ELECTRONIC DATA PROCESSING
The Three Types of Data Processing System
Manual Data Processing System: Data are processed manually.
Mechanical Data Processing System: Data are processed by machine.
Electronic Data Processing (EDP) System: Data are processed by computer.
The Advantages of EDP
--accurate
--fast
--large storage
--never get tired
--number of staff and cost can be reduced
Criteria for Computerization
The amount of data, the cost of computerization and the computer knowledge of the
staff should be considered for the possibility of computerization.
The criteria for computerization:
--a large amount of data
--the cost of computerization does not exceed the budget
--the staff must know how to operate a computer
1
Stages of Computerization
(A) (1) Preliminary Study
-- identify the problems of current data processing system and the needs for a
new electronic data processing system.
(2) Feasibility Study
--consider the feasibility of computerization based on the criteria such as the
amount of money and the ability of staff.
--find out if there are other better approaches.
(B) (1) System Analysis
--Analyze the working procedures of current data processing system.
(2) System Design
-- Design the working procedures(data collection methods, security measures,
file organizations and output formats, etc.) of the new electronic data
processing system.
(3) System Implementation
(a) Programming
--write and test the programs.
(b) System testing
--test the new EDP system with real data.
(c) System documentation
--produce documents (user manuals) to describe the EDP system to
users.
(d) User training
--train users to use the computers.
(e) Changeover
--replace the old system by the new EDP system.
2
(4) System Maintenance and Evaluation
--evaluate and modify the EDP system in the future.
Data Control in EDP
Garbage In Garbage Out (GIGO):
If the input data is incorrect, the output result will also be incorrect.
There are two main types of data control:
(A) Verification of data
--it is done in the data preparation stage
--it is done by double checking
--it is used to ensure the data is correct
(B) Validation of data
--it is done in the data input stage
--it is done by validation program
--it is used to ensure the data is reasonable
Techniques of data validation:
(1) Field Check
--check the data type, size and presence
Eg. (a) name should not consist of number:
CHAN TA5 MAN
(b) telephone number should not contain less than 7 digits:
568481
(2) Range Check
--check whether the data is within the range
3
Eg. exam marks should not be negative:
-15
(3) Reasonableness Check
(4) Control Total
(5) Check Digit
Example:
K905915 is an ID card number using weights 8,7,6,5,4,3,2 with modulus 11.
(Note: K = 11) What is the check digit?
Step (1):
(11)
ID number: K 9 0 5 9 1 5
      
weights: 8 7 6 5 4 3 2
Step (2):
Sum = 11*8 + 9*7 + 0*6 + 5*5 + 9*4 + 1*3 + 5*2 = 225
20
------11) 225
22
-----5 <--- Remainder
Step (3):
4
Check Digit = 11 - 5 = 6
ID card number = K905915(6)
System Flowchart
System flowchart shows the flow of data and the sequence of operations in a data
processing system by arrows (flowlines) and symbols.
Computer Communication and Networking
Computer Network:
A computer network is a number of computers interconnected together by means of
communication links so as to permit sharing of resources between computers.
Advantages of Computer Network:
(1) Resource Sharing
--both software and peripherals can be shared by different computers.
(2) Load Sharing
--when one computer gets heavily loaded, its work can be transferred to other
computers so as to improve the speed of the whole system.
--similarly, when one computer fails to work, another computer in the network can
take over its job.
(3) Distributed Processing
--various steps of a job can be performed on different computers in the network
(workstations) by means of parallel processing (multi-processing).
5
(4) Exchange Information
--data can be accessed by different computers in the network.
(5) Organization Benefit
--computer network can enhance the systematization of administration job in an
organization.
(In general, the major reasons for computer networking are the sharing of resources
(hardware/software) and the communication of data/information between computers)
Types of Computer Network
Computer Networks can be differed in:
(a) Network Size
(b) Data Communication Channel
(c) Network Topology
(d) Mode of Data Transfer
(A) Two Basic Types of Computer Network:
(1) Local Area Network (LAN)
--The linking of computers over a small area (eg. a single room, a building or a group
of buildings).
(2) Wide Area Network (WAN)
--The linking of a larger number of computers over a large area to a mainframe
(different sites, different cities or countries).
Examples of WAN: (a) Automatic Teller Machines (ATM)
(b) Easy Paid System (EPS)
6
(c) Electronic Mail
(B) Basic Components of a Computer Network
Cables (Data Communication Channels):
(1) Twisted-pair Cable (Telephone Lines)
(2) Coaxial Cable
(3) Fibre Optic Cable
Network Interface Card:
-- A circuit board responsible for the sending and receiving messages.
Network Server:
-- A combination of software and hardware to manage the shared resources in the
network.
Central Storage:
-- A large hard disk which stores the files and data shared by the workstations in the
network.
Workstations:
-- The workstations can be "dumb" terminals (with keyboard and VDU only) or
microcomputers.
Modem (used in WAN only):
-- A device which converts digital signal to analog signal and converts analog signal to
digital signal.
7
(C) Network Topology
(1) Star Topology:
-- the nodes (terminals/peripherals) are connected to a host computer (mainframe).
-- any signal is sent to the host first.
-- the system can work as long as the host is well functioned.
(2) Bus Topology:
-- all the nodes are connected to a single bus.
-- when a signal is sent out, all the nodes on the network can receive it.
-- any node can break down without affecting other nodes.
(3) Ring Topology:
-- the nodes are arranged in a circle.
-- the signal is passed from one node to another node and so on during
communication.
-- if one node breaks down, the whole network breaks down.
8