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what is data representation

External data representation and marshalling

External data representation and marshalling

Data
The word data is derived from Latin language. It is plural of Datum (But Data is usually used as a singular term.) Datum (singular) – Data (plural). Data is any collection of facts of figures. The data is the raw material to be processed by a computer.
Example
Names of students, marks obtained in the examination, designation of employees, addresses, quantity, rate, sales figures or anything that is input to the computer is data. Even pictures, photographs, drawings, charts and maps can be treated as data. Computer processes the data and produces the output or result.

Types of Data
Mainly Data is divided into two types:
1. Numeric Data
2. Character Data

Numeric Data

The data which is represented in the form of numbers is known as Numeric Data. This includes 0-9 digits, a decimal point (.), +, /, – sign and the letters “E” or “D”. The numeric data is further divided into two groups:
1. Integer Data
2. Real Data

Integer Data
Integer Data is in the form of whole numbers. It does not contain a decimal point, however it may be a positive or a negative number.
Example
Population of Pakistan, numbers of passengers traveling in an airplane, number of students in a class, number of computer in a lab etc.
2543, 7, -60, 5555, 0, + 72 etc

Real Data
Real data is in the form of fractional numbers. It contains a decimal point. It can also be positive or negative number.
Real Data is further divided into two types.
a. Fixed Point Data
b. Floating Point Data

(a) Fixed Point Data

Fixed point data may include digits (0–9), a decimal point, + / – sign.
Example
Percentage of marks, weight, quantity temperature etc.
-23.0007, 0.0002, + 9243.9, 17013 etc

(b) Floating Point Data
Floating point data may include digits (0-9), decimal point, + / – sign and letters “D”, “d”, “E”, or “e”. The data, which is in the exponential form, can be represented in the floating point notation.
Example
Speed of light, mass of atomic particles, distance between stars and etc.
1.602 x 10(-19) (Charge of electron in coulomb) – Here -19 = power
The value can be feed into the computer as 1.602 E-19.

Character Data
Character data falls into two groups.
1. String Data
2. Graphical Data

String Data
String data consists of the sequence of characters. Characters may be English alphabets, numbers or space. The space, which separates two words, is also a character. The string data is further divided into two types.
1. Alphabetic Data
2. Alphanumeric Data

(a) Alphabetic Data
The data, which is composed of English alphabets, is called alphabetic data. Names of people, names of places, and names of items are considered alphabetic data.
For example : Ahmed, Hyderabad, Chair etc

(b) Alphanumeric Data

The data that consists of alphabets as well as numerals and some special characters is called alphanumeric data. Address, employee’s code, etc are alphanumeric data.
For example: 10/B, Block No 2, E103 etc.

Graphical Data
It is possible that pictures, charts and maps can be treated as data. The scanner is normally used to enter this type of data. The common use of this data is found in the National Identity Card. The photographs and thumb impression are scanned and stored into the computer to identify a person.

Number System
The number system is the system of counting and calculation. Number system is based on some characters called digits. Each number is made up of these characters. The number of digits a sysem uses is called its base or radix. For example the number system we use in our daily life is called Decimal System. Its base is 10 (As the name ‘Deci’ implies which mean that it uses 10 digits (i.e. 0-9)

Codes
When numbers, letters or words are represented by a special group of symbols, we say they are being encoded and the group of system is called “Code”.

Types of Codes
The codes include Binary code, Binary-coded-decimal code (BCD), and alpha numeric codes. Alphanumeric codes include ASCII and EBCDIC.

ASCII Code
ASCII stands for American Standard Code for Information Interchange. It is a 7-bit code used to handle alphanumeric data. This code allows manufacturers to standardize input/output devices such as keyboard, printers, visual display units etc. An extension of ASCII code uses 8-bits called as ASCII-8 code with an extra 8th-bit as a parity bit to make the total number of 1’s either odd or even.

EBCDIC Code
EBCDIC (Extended Binary Coded Decimal Interchange Code) is an extended form of BCD (Binary Coded Decimal), which can represent only 16 characters because it is a 4-bit code. EBCDIC is an 8-bit code, so it can represent 256 different characters. It was developed by IBM and is used in most IBM models and many other computers.

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