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In Communication s, a code is a Rule for converting a piece of Information (for example, a Letter , Word , or Phrase ) into another form or representation, not necessarily of the same type. In Communication s and Information Processing , '''encoding''' is the Process by which information from a Source is converted into symbols to be communicated. '''Decoding''' is the reverse process, converting these code symbols back into information understandable by a receiver. One reason for coding is to enable communication in places where ordinary spoken or written language is difficult or impossible. For example, a cable code replaces words (e.g., ''ship'' or ''invoice'') into shorter words, allowing the same information to be sent with fewer Characters , more quickly, and most important, less expensively. Another example is the use of Semaphore Flags , where the configuration of flags held by a signaller or the arms of a semaphore tower encodes parts of the message, typically individual letters and numbers. Another person standing a great distance away can interpret the flags and reproduce the words sent. In the History Of Cryptography , codes were once common for ensuring the confidentiality of communications, although Cipher s are now used instead. See Code (cryptography) . CODES IN COMMUNICATION USED FOR BREVITY Code can be used for brevity. When telegraph messages were the state of the art in rapid long distance communication, elaborate commercial codes which encoded complete phrases into single words (commonly five-letter groups) were developed, so that run by Herbert Yardley between WWI and WWII. The purpose of most of these codes was to save on cable costs. The use of data coding for Data Compression predates the computer era; an early example is the Telegraph Morse Code where more frequently-used characters have shorter representations. Techniques such as Huffman Coding are now used by computer-based algorithms to compress large data files into a more compact form for storage or transmission. AN EXAMPLE: THE ASCII CODE Probably the most widely known data communications code (aka character representation) in use today is ASCII . In one or another (somewhat compatible) version, it is used by nearly all personal Computer s, Terminals , Printers , and other communication equipment. Its original version represents 128 Characters with seven-bit Binary numbers—that is, as a string of seven 1s and 0s. In ASCII a lowercase "a" is always 1100001, an uppercase "A" always 1000001, and so on. Successors to ASCII have included 8-bit characters (for letters of European languages and such things as card suit symbols), and in fullest flowering have included glyphs from essentially all of the world's writing systems (see Unicode and UTF-8 ). CODES TO DETECT OR CORRECT ERRORS Codes may also be used to represent data in a way more resistant to errors in transmission or storage. Such a "code" is called an Error-correcting Code , and works by including carefully crafted redundancy with the stored (or transmitted) data. Examples include Hamming Code s, Reed–Solomon , Reed–Muller , Bose–Chaudhuri–Hochquenghem , Turbo , Golay , Goppa , Gallager Low-density Parity-check Code s, and Space–time Code s. Error detecting codes can be optimised to detect ''burst errors'', or ''random errors''. CODES AND ACRONYMS Acronym s and abbreviations can be considered codes, and in a sense all Language s and writing systems are codes for human thought. Occasionally a code word achieves an independent existence (and meaning) while the original equivalent phrase is forgotten or at least no longer has the precise meaning attributed to the code word. For example, '30' was widely used in Journalism to mean "end of story", and it is sometimes used in other contexts to signify "the end". GöDEL CODE In Mathematics , a Gödel Code was the basis for the proof of Gödel 's Incompleteness Theorem . Here, the idea was to map Mathematical Notation to a Natural Number (a Gödel Number ). SEE ALSO United States Government Code: A form of communication used by government personnel to communicate their wishes for kickbacks. |
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