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Ch.2 Data organization and control (2.4 Database Management System…
Ch.2 Data organization and control
2.1
Data Input and Source of Errors
Data can be inputted by various means
Wrong input = inaccurate output (GIGO)
types of errors
data source error
transcription error
e.g. 1 is inputted as l
transposition error
e.g. 61 is inputted as 16
e.g. keyboards, sensors, scanners etc.
2.2
Data control (reduce data errors)
Data validation: compare data with rules to make sure it is valid
Using various validity check e.g. field presence check, check digit...
Data verification: check if input data matches source document
Input data twice: 1 person inputs data twice to check against each other
Double data entry: 2 operators enter the data into different files, computer checks them against each other
2.3 Data Hierarchy
data is organised by a hierachy
field
can be numeric, text, date etc.
(e.g. phone no.)
record
a collection of related fields
table
a collection of related records with identical record structures
database
A collection of related tables
2.4 Database Management System
DBMS: computer program
e.g. MySQL
Use: manage database structure &
store,organize and retrieve data in database
Database
Tables
Record
Fields
2.5 File Access Modes
Programs accessed by either sequential access mode or direct access
Sequential Access Mode
mainly used for backing up or recovering data
Direct Access Mode
most common storage due to its high reliability, speed and capacity
[both are corrected manually]