Code 5225 225829154 2008-07-15T16:19:35Z Epbr123 1395162 Reverted edits by [[Special:Contributions/OrgasGirl|OrgasGirl]] to last version by 74.7.3.202 (using [[WP:HG|Huggle]]) {{otheruses}} In [[communication]]s, a '''code''' is a [[Operator|rule]] for converting a piece of [[information]] (for example, a [[Letter (alphabet)|letter]], [[word]], [[phrase]], or [[gesture]]) into another form or representation (one [[sign]] into another sign), not necessarily of the same type. In communications and [[information processing]], '''encoding''' is the [[Process (general)|process]] by which information from a [[communication source|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, semaphore, where the configuration of [[Flag semaphore|flags]] held by a signaller or the arms of a [[semaphore line|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== A cable code replaces words (e.g., ''ship'' or ''invoice'') into shorter words, allowing the same information to be sent with fewer [[character (computing)|characters]], more quickly, and most important, less expensively. 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 [[Telegraphy|telegraphers]] became conversant with such "words" as ''BYOXO'' ("Are you trying to weasel out of our deal?"), ''LIOUY'' ("Why do you not answer my question?"), ''BMULD'' ("You're a skunk!"), or ''AYYLU'' ("Not clearly coded, repeat more clearly."). [[Code word]]s were chosen for various reasons: [[length]], [[pronounceability]], etc. Meanings were chosen to fit perceived needs: commercial negotiations, military terms for military codes, diplomatic terms for diplomatic codes, any and all of the preceding for espionage codes. Codebooks and codebook publishers proliferated, including one run as a front for the American [[Black Chamber]] 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 [[Telegraphy|telegraph]] [[Morse code]] where more frequently-used characters have shorter representations. Techniques such as [[Huffman coding]] are now used by computer-based [[algorithm]]s to compress large data files into a more compact form for storage or transmission. <!--In the computer era since World War II, there are also "codes" for [[data compression]], e.g. [[Huffman coding]], which uses short codes for frequent [[symbol]]s and longer codes for seldom used symbols - the same principle is used in the [[Morse code]]. It and the [[Baudot code]] which uses the same length [[representation]] for all symbols and characters, both go back to telegraph days. The latter was a primary ancestor of the ASCII character code widely used in computers. --> ==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, [[computer terminal|terminals]], [[computer printer|printers]], and other communication equipment. It represents 128 [[character (computing)|characters]] with seven-bit [[Binary numeral system|binary]] numbers&mdash;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 characters from essentially all of the world's writing systems (see [[Unicode]] and [[UTF-8]]). ==Codes to detect or correct errors== {{main|Error detection and correction}} 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 correction and detection|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]], [[BCH code|Bose–Chaudhuri–Hochquenghem]], [[Turbo code|Turbo]], [[Golay code|Golay]], [[Goppa code|Goppa]], [[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". ==Coupon Codes== In [[marketing]], [[coupon]] codes can be used for a financial discount or rebate when purchasing a product from an internet retailer. Coupon codes are also referred to as "promotional codes," "promotion codes," "discount codes," "key codes," "promo codes," "shopping codes," "voucher codes" or "source codes."<ref name="couponcode">[http://www.freeshipping.org/blog/history-of-coupons/ The History of Coupons]</ref> ==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]]). ==References== {{reflist}} ==See also== {{commonscat|Codes|Codes}} *[[List of coding terms]] *[[Asemic writing]] *[[Semiotics]] [[Category:Encodings]] [[da:Kode]] [[de:Code]] [[el:Κώδικας]] [[es:Código]] [[eo:Kodo]] [[fr:Code (information)]] [[ko:인코딩]] [[hr:Kod]] [[id:Kode]] [[it:Codice (teoria dell'informazione)]] [[he:קוד]] [[nl:Code]] [[ja:符号]] [[no:Kode]] [[pl:Kod]] [[pt:Código]] [[ru:Код]] [[simple:Code]] [[sk:Kód]] [[th:รหัส]] [[uk:Код]]