Data Representation

Alphanumeric Representation

Definition  

• It is a set of characters containing alphabets (A-Z, a-z), the decimal digits (0-9) and special characters/symbols (roughly 10-15 in numbers) consist of at least 80-100 elements.
• Alphanumeric Characters are represented in computer in following form – 

ASCII Representation 

• It is one of the International standard code that allows the language encoding in numeric form that is popularly called ASCII (American Standard Code for Information Interchange)code.
• This code uses 7 bits representation to encode 128 characters, which include 32 non-printing control characters, alphabets in lower and upper case, decimal digits, and other printable characters that are available on our keyboard.
• Later, ASCII was extended to 8 bits formats to represent 256 new modern characters (called Extended ASCII codes) which additionally include graphics characters, additional special characters etc.In the original, the 8th bit of ASCII (the most significant bit) was used for the purpose of error checking as a check bit.This extended ASCII codes are used in most of the Microcomputers.
• The major strength of ASCII is that it is quite elegant in the way it represents characters in computers.It is easy to write a code using ASCII format to manipulate upper/lowercase ASCII characters and check for valid data ranges because of the way of representation of characters.

EBCDIC Representation

• Extended Binary Coded Decimal Interchange Code (EBCDIC) is also a character-encoding format developed by IBM.
• This was primarily used on IBM mainframes and mid range systems.
• It is an 8-bit code and is NOT Compatible to ASCII.
• It had been designed primarily for ease of use of punched cards.
• Another strength of EBCDIC was the availability of wider range of control characters for ASCII.
• The character coding in this format is based on binary coded decimal, that is, the contiguous characters in the alphanumeric range are represented in blocks of 10 starting from 0000 binary to 1001 binary.Other characters fill in the rest of the range.

0000 0000 to 0011 1111	Used for control characters
0100 0000 to 0111 1111	Punctuation characters
1000 0000 to 1011 1111	Lowercase characters
1100 0000 to 1111 1111	Uppercase characters and numbers.

• EBCDIC is an easier to use code on punched cards because of BCD compatibility.
• There are several different variants of EBCDIC. Most of these differ in the punctuation coding.
• While writing a code using EBCDIC, which is not contiguous on alphabets, data comparison to continuous character blocks is not easy than ASCII.
• Some of the symbol/control characters such as [ ] \ { } ^ ~ | etc. are missing in EBCDIC that may cause some incompatibility problems.

UNICODE Representation

• This is a newer International standard for character representation.
• Unicode provides a unique code for every character, irrespective of the platform, program and language.
• Unicode Standard has been adopted by the Industry such as Apple, HP, IBM, Microsoft, Oracle, SAP, Sun, Sybase, Unisys and many other companies.
• Unicode has been implemented in most of the latest client server software.
• Unicode is required by modern standards such as XML, Java, JavaScript, CORBA 3.0, etc.
• It is supported in many operating systems, and almost all modern web browsers.
• Unicode includes character set of Dev Nagari.
• The emergence of the Unicode Standard, and the availability of tools supporting it, is among the most significant recent global software technology trends.
• One of the major advantages of Unicode in the client-server or multi-tiered applications and websites is the cost saving over the use of legacy character sets that results in targeting website and software products across multiple platforms, languages and countries without re-engineering. Thus, it helps in data transfer through many different systems without any compatibility problems. In India the suitability of Unicode to implement Indian languages is still being worked out.

ISCII Representation

• ISCII stands for Indian Standard Code for information interchange. 
• The ISCII is an eight-bit code that contains the standard ASCII values till 127 from 128-225.
• It contains the characters required in the ten Brahmi-based Indian scripts.
• It is defined in IS 13194:1991 BIS standard.
• It supports INSCRIPT keyboard which provides a logical arrangement of vowels and consonants based on the phonetic properties and usage frequencies of the letters of Bramhi-scripts. Thus, allowing use of existing English keyboard for Indian language input.
• Any software that uses ISCII codes can be used in any Indian Script, enhancing its commercial viability.
• It also allows transliteration between different Indian scripts through change of display mode.