Code
Encyclopedia
A code is a rule for converting a piece of information
(for example, a letter
, word
, phrase
, or gesture
) into another form or representation (one sign
into another sign), 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, semaphore, where the configuration of flags
held 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.
and computer science
, a code is usually considered as an algorithm
which uniquely represents symbols from some source alphabet, by encoded strings, which may be in some other target alphabet. An extension of the code for representing sequences of symbols over the source alphabet is obtained by concatenating the encoded strings.
Before giving a mathematically precise definition, we give a brief example. The mapping
is a code, whose source alphabet is the set
and whose target alphabet is the set 
. Using the extension of the code, the encoded string 0011001011 can be grouped into codewords as 0 – 011 – 0 – 01 – 011, and these in turn can be decoded to the sequence of source symbols acabc.
Using terms from formal language theory, the precise mathematical definition of this concept is as follows: Let S and T be two finite sets, called the source and target alphabets, respectively. A code
is a total function mapping each symbol from S to a sequence of symbols
over T, and the extension of M to a homomorphism of
into 
, which naturally maps each sequence of source symbols to a sequence of target symbols, is referred to as its extension.
from some dictionary, and concatenation
of such code words give us an encoded string.
Variable-length codes are especially useful when clear text characters have different probabilities; see also entropy encoding
.
A prefix code is a code with the "prefix property": there is no valid code word
in the system that is a prefix (start) of any other valid code word in the set. Huffman coding
is the most known algorithm for deriving prefix codes, so prefix codes are also widely referred to as "Huffman codes", even when the code was not produced by a Huffman algorithm.
Other examples of prefix codes are country calling codes, the country and publisher parts of ISBNs, and the Secondary Synchronization Codes used in the UMTS W-CDMA
3G Wireless Standard.
Kraft's inequality
characterizes the sets of code word lengths that are possible in a prefix code. Virtually, any uniquely decodable one-to-many code, not necessary a prefix one, must satisfy Kraft's inequality.
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, Walsh–Hadamard, Bose–Chaudhuri–Hochquenghem
, Turbo
, Golay, 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.
, more quickly, and most important, less expensively.
Codes can be used for brevity. When telegraph messages were the state of the art in rapid long distance communication, elaborate systems of commercial codes that encoded complete phrases into single words (commonly five-letter groups) were developed, so that 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 the First and Second World Wars. 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 algorithm
s to compress large data files into a more compact form for storage or transmission.
. In one or another (somewhat compatible) version, it is used by nearly all personal computer
s, terminals
, printers
, and other communication equipment. It represents 128 characters
with seven-bit binary
numbers—that is, as a string of seven 1s and 0s. In ASCIIvcx a lowercase "a" is always 1100001, an uppercase "A" always 1000001, and so on. There are many other encodings, which represent each character by a byte
(usually referred as code page
s), integer code point
(Unicode
) or a byte sequence (UTF-8
).
organisms contain genetic material that is used to control their function and development. This is DNA
which contains units named genes
that can produce proteins through a code (genetic code
) in which a series of triplets {codons} of four possible nucleotides are translated into one of twenty possible amino acids. A sequence of codons results in a corresponding sequence of amino acids that form a protein.
, 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
(using a Gödel numbering).
employed to mark the nominal value of the electrical resistor
s or that of the trashcans devoted to specific types of garbage (paper, glass, biological, etc.)
In marketing
, coupon
codes can be used for a financial discount or rebate when purchasing a product from an internet retailer.
In military environments, specific sounds with the cornet
are used for different uses: to mark some moments of the day, to command the infantry in the battlefield, etc.
Communication systems for sensory impairments, as the sign language
for deaf people and braille
for blind people, are based in movement or tactile codes.
Musical scores are the most common way to encode music
.
Specific games, as chess
, have their own code systems to record the matches (chess notation
).
, codes were once common for ensuring the confidentiality of communications, although cipher
s are now used instead. See code (cryptography)
.
Secret code
s intended to obscure the real messages, ranging from serious (mainly espionage in military, diplomatic, business, etc.) to trivial (romance, games) can be any kind of imaginative encoding: flowers, game cards, clothes, fans, hats, melodies, birds, etc., in which the sole requisite is the previous agreement of the meaning by both the sender and the receiver.
Other examples of decoding include:
s and writing systems are codes for human thought.
International Air Transport Association airport codes are three-letter codes used to designate airports and used for bag tag
s.
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".
Information
Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...
(for example, a letter
Letter (alphabet)
A letter is a grapheme in an alphabetic system of writing, such as the Greek alphabet and its descendants. Letters compose phonemes and each phoneme represents a phone in the spoken form of the language....
, word
Word
In language, a word is the smallest free form that may be uttered in isolation with semantic or pragmatic content . This contrasts with a morpheme, which is the smallest unit of meaning but will not necessarily stand on its own...
, phrase
Phrase
In everyday speech, a phrase may refer to any group of words. In linguistics, a phrase is a group of words which form a constituent and so function as a single unit in the syntax of a sentence. A phrase is lower on the grammatical hierarchy than a clause....
, or gesture
Gesture
A gesture is a form of non-verbal communication in which visible bodily actions communicate particular messages, either in place of speech or together and in parallel with spoken words. Gestures include movement of the hands, face, or other parts of the body...
) into another form or representation (one sign
Sign
A sign is something that implies a connection between itself and its object. A natural sign bears a causal relation to its object—for instance, thunder is a sign of storm. A conventional sign signifies by agreement, as a full stop signifies the end of a sentence...
into another sign), not necessarily of the same type.
In communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
s and information processing
Information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...
, encoding is the process by which information from a source
Communication source
A source or sender is one of the basic concepts of communication and information processing. Sources are objects which encode message data and transmit the information, via a channel, to one or more observers ....
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 flags
Flag semaphore
Semaphore Flags is the system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position...
held 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.
Theory
In information theoryInformation theory
Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...
and computer science
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, a code is usually considered as an algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
which uniquely represents symbols from some source alphabet, by encoded strings, which may be in some other target alphabet. An extension of the code for representing sequences of symbols over the source alphabet is obtained by concatenating the encoded strings.
Before giving a mathematically precise definition, we give a brief example. The mapping
is a code, whose source alphabet is the set
and whose target alphabet is the set . Using the extension of the code, the encoded string 0011001011 can be grouped into codewords as 0 – 011 – 0 – 01 – 011, and these in turn can be decoded to the sequence of source symbols acabc.Using terms from formal language theory, the precise mathematical definition of this concept is as follows: Let S and T be two finite sets, called the source and target alphabets, respectively. A code
is a total function mapping each symbol from S to a sequence of symbolsString (computer science)
In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....
over T, and the extension of M to a homomorphism of
into , which naturally maps each sequence of source symbols to a sequence of target symbols, is referred to as its extension.Variable-length codes
In this section we consider codes, which encode each source (clear text) character by a code wordCode word
In communication, a code word is an element of a standardized code or protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning...
from some dictionary, and concatenation
Concatenation
In computer programming, string concatenation is the operation of joining two character strings end-to-end. For example, the strings "snow" and "ball" may be concatenated to give "snowball"...
of such code words give us an encoded string.
Variable-length codes are especially useful when clear text characters have different probabilities; see also entropy encoding
Entropy encoding
In information theory an entropy encoding is a lossless data compression scheme that is independent of the specific characteristics of the medium....
.
A prefix code is a code with the "prefix property": there is no valid code word
Code word
In communication, a code word is an element of a standardized code or protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning...
in the system that is a prefix (start) of any other valid code word in the set. Huffman coding
Huffman coding
In computer science and information theory, Huffman coding is an entropy encoding algorithm used for lossless data compression. The term refers to the use of a variable-length code table for encoding a source symbol where the variable-length code table has been derived in a particular way based on...
is the most known algorithm for deriving prefix codes, so prefix codes are also widely referred to as "Huffman codes", even when the code was not produced by a Huffman algorithm.
Other examples of prefix codes are country calling codes, the country and publisher parts of ISBNs, and the Secondary Synchronization Codes used in the UMTS W-CDMA
W-CDMA
W-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
3G Wireless Standard.
Kraft's inequality
Kraft's inequality
In coding theory, Kraft's inequality, named after Leon Kraft, gives a necessary and sufficient condition for the existence of a uniquely decodable code for a given set of codeword lengths...
characterizes the sets of code word lengths that are possible in a prefix code. Virtually, any uniquely decodable one-to-many code, not necessary a prefix one, must satisfy Kraft's inequality.
Error correcting codes
Codes may also be used to represent data in a way more resistantto 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
Hamming code
In telecommunication, Hamming codes are a family of linear error-correcting codes that generalize the Hamming-code invented by Richard Hamming in 1950. Hamming codes can detect up to two and correct up to one bit errors. By contrast, the simple parity code cannot correct errors, and can detect only...
s, Reed–Solomon, Reed–Muller, Walsh–Hadamard, Bose–Chaudhuri–Hochquenghem
BCH code
In coding theory the BCH codes form a class of parameterised error-correcting codes which have been the subject of much academic attention in the last fifty years. BCH codes were invented in 1959 by Hocquenghem, and independently in 1960 by Bose and Ray-Chaudhuri...
, Turbo
Turbo code
In information theory, turbo codes are a class of high-performance forward error correction codes developed in 1993, which were the first practical codes to closely approach the channel capacity, a theoretical maximum for the code rate at which reliable communication is still possible given a...
, Golay, Goppa, low-density parity-check code
Low-density parity-check code
In information theory, a low-density parity-check code is a linear error correcting code, a method of transmitting a message over a noisy transmission channel, and is constructed using a sparse bipartite graph...
s, and space–time code
Space–time code
A space–time code is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas...
s.
Error detecting codes can be optimised to detect burst errors, or random errors.
Codes in communication used for brevity
A cable code replaces words (e.g., ship or invoice) with shorter words, allowing the same information to be sent with fewer charactersCharacter (computing)
In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....
, more quickly, and most important, less expensively.
Codes can be used for brevity. When telegraph messages were the state of the art in rapid long distance communication, elaborate systems of commercial codes that encoded complete phrases into single words (commonly five-letter groups) were developed, so that telegraphers
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...
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
Code word
In communication, a code word is an element of a standardized code or protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning...
s were chosen for various reasons: length
Length
In geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...
, 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
Black Chamber
The Cipher Bureau otherwise known as The Black Chamber was the United States' first peacetime cryptanalytic organization, and a forerunner of the National Security Agency...
run by Herbert Yardley
Herbert Yardley
Herbert Osborne Yardley was an American cryptologist best known for his book The American Black Chamber . The title of the book refers to the Cipher Bureau, the cryptographic organization of which Yardley was the founder and head...
between the First and Second World Wars. The purpose of most of these codes was to save on cable costs. The use of data coding for data compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
predates the computer era; an early example is the telegraph
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...
Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
where more-frequently used characters have shorter representations. Techniques such as Huffman coding
Huffman coding
In computer science and information theory, Huffman coding is an entropy encoding algorithm used for lossless data compression. The term refers to the use of a variable-length code table for encoding a source symbol where the variable-length code table has been derived in a particular way based on...
are now used by computer-based algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
s to compress large data files into a more compact form for storage or transmission.
Character encodings
Probably the most widely known data communications code so far (aka character representation) in use today is ASCIIASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
. In one or another (somewhat compatible) version, it is used by nearly all personal computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s, terminals
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
, printers
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...
, and other communication equipment. It represents 128 characters
Character (computing)
In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....
with seven-bit binary
Binary numeral system
The binary numeral system, or base-2 number system, represents numeric values using two symbols, 0 and 1. More specifically, the usual base-2 system is a positional notation with a radix of 2...
numbers—that is, as a string of seven 1s and 0s. In ASCIIvcx a lowercase "a" is always 1100001, an uppercase "A" always 1000001, and so on. There are many other encodings, which represent each character by a byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
(usually referred as code page
Code page
Code page is another term for character encoding. It consists of a table of values that describes the character set for a particular language. The term code page originated from IBM's EBCDIC-based mainframe systems, but many vendors use this term including Microsoft, SAP, and Oracle Corporation...
s), integer code point
Code point
In character encoding terminology, a code point or code position is any of the numerical values that make up the code space . For example, ASCII comprises 128 code points in the range 0hex to 7Fhex, Extended ASCII comprises 256 code points in the range 0hex to FFhex, and Unicode comprises 1,114,112...
(Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
) or a byte sequence (UTF-8
UTF-8
UTF-8 is a multibyte character encoding for Unicode. Like UTF-16 and UTF-32, UTF-8 can represent every character in the Unicode character set. Unlike them, it is backward-compatible with ASCII and avoids the complications of endianness and byte order marks...
).
Genetic code
BiologicalBiology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
organisms contain genetic material that is used to control their function and development. This is DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
which contains units named genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
that can produce proteins through a code (genetic code
Genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
) in which a series of triplets {codons} of four possible nucleotides are translated into one of twenty possible amino acids. A sequence of codons results in a corresponding sequence of amino acids that form a protein.
Gödel code
In mathematicsMathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
, a Gödel code was the basis for the proof of Gödel
Godel
Godel or similar can mean:*Kurt Gödel , an Austrian logician, mathematician and philosopher*Gödel...
's incompleteness theorem. Here, the idea was to map mathematical notation
Mathematical notation
Mathematical notation is a system of symbolic representations of mathematical objects and ideas. Mathematical notations are used in mathematics, the physical sciences, engineering, and economics...
to a natural number
Natural number
In mathematics, the natural numbers are the ordinary whole numbers used for counting and ordering . These purposes are related to the linguistic notions of cardinal and ordinal numbers, respectively...
(using a Gödel numbering).
Other
There are codes using colors, like traffic lights, the color codeElectronic color code
The electronic color code is used to indicate the values or ratings of electronic components, very commonly for resistors, but also for capacitors, inductors, and others...
employed to mark the nominal value of the electrical resistor
Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
s or that of the trashcans devoted to specific types of garbage (paper, glass, biological, etc.)
In marketing
Marketing
Marketing is the process used to determine what products or services may be of interest to customers, and the strategy to use in sales, communications and business development. It generates the strategy that underlies sales techniques, business communication, and business developments...
, coupon
Coupon
In marketing, a coupon is a ticket or document that can be exchanged for a financial discount or rebate when purchasing a product. Customarily, coupons are issued by manufacturers of consumer packaged goods or by retailers, to be used in retail stores as a part of sales promotions...
codes can be used for a financial discount or rebate when purchasing a product from an internet retailer.
In military environments, specific sounds with the cornet
Cornet
The cornet is a brass instrument very similar to the trumpet, distinguished by its conical bore, compact shape, and mellower tone quality. The most common cornet is a transposing instrument in B. It is not related to the renaissance and early baroque cornett or cornetto.-History:The cornet was...
are used for different uses: to mark some moments of the day, to command the infantry in the battlefield, etc.
Communication systems for sensory impairments, as the sign language
Sign language
A sign language is a language which, instead of acoustically conveyed sound patterns, uses visually transmitted sign patterns to convey meaning—simultaneously combining hand shapes, orientation and movement of the hands, arms or body, and facial expressions to fluidly express a speaker's...
for deaf people and braille
Braille
The Braille system is a method that is widely used by blind people to read and write, and was the first digital form of writing.Braille was devised in 1825 by Louis Braille, a blind Frenchman. Each Braille character, or cell, is made up of six dot positions, arranged in a rectangle containing two...
for blind people, are based in movement or tactile codes.
Musical scores are the most common way to encode music
Music
Music is an art form whose medium is sound and silence. Its common elements are pitch , rhythm , dynamics, and the sonic qualities of timbre and texture...
.
Specific games, as chess
Chess
Chess is a two-player board game played on a chessboard, a square-checkered board with 64 squares arranged in an eight-by-eight grid. It is one of the world's most popular games, played by millions of people worldwide at home, in clubs, online, by correspondence, and in tournaments.Each player...
, have their own code systems to record the matches (chess notation
Chess notation
Chess notation is the term for several systems that have developed to record either the moves made during a game of chess or the position of the pieces on a chess board. The earliest systems of notation used lengthy narratives to describe each move; these gradually evolved into terser systems of...
).
Cryptography
In the history of cryptographyHistory of cryptography
The history of cryptography begins thousands of years ago. Until recent decades, it has been the story of what might be called classic cryptography — that is, of methods of encryption that use pen and paper, or perhaps simple mechanical aids...
, codes were once common for ensuring the confidentiality of communications, although cipher
Cipher
In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...
s are now used instead. See code (cryptography)
Code (cryptography)
In cryptography, a code is a method used to transform a message into an obscured form, preventing those who do not possess special information, or key, required to apply the transform from understanding what is actually transmitted. The usual method is to use a codebook with a list of common...
.
Secret code
Secret Code
Secret Code is the debut major album of artist Aya Kamiki, released on July 12, 2006. It comes in a CD only version. Secret Code debuted at number 5 on the Oricon Weekly Charts for Japan and sold 65,004 copies in total...
s intended to obscure the real messages, ranging from serious (mainly espionage in military, diplomatic, business, etc.) to trivial (romance, games) can be any kind of imaginative encoding: flowers, game cards, clothes, fans, hats, melodies, birds, etc., in which the sole requisite is the previous agreement of the meaning by both the sender and the receiver.
Other examples
Other examples of encoding include:- Encoding (in cognitionCognitionIn science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
) is a basic perceptual process of interpreting incoming stimuli; technically speaking, it is a complex, multi-stage process of converting relatively objective sensory input (e.g., light, sound) into subjectively meaningful experience. - A content formatContent formatA content format is an encoded format for converting a specific type of data to displayable information. Content formats are used in recording and transmission to prepare data for observation or interpretation. This includes both analog and digitized content...
is a specific encoding format for converting a specific type of dataDataThe term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
to informationInformationInformation in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...
. - Text encoding uses a markup languageMarkup languageA markup language is a modern system for annotating a text in a way that is syntactically distinguishable from that text. The idea and terminology evolved from the "marking up" of manuscripts, i.e. the revision instructions by editors, traditionally written with a blue pencil on authors' manuscripts...
to tag the structure and other features of a text to facilitate processing by computers. (See also Text Encoding InitiativeText Encoding InitiativeThe Text Encoding Initiative is a text-centric community of practice in the academic field of digital humanities. The community runs a mailing list, meetings and conference series, and maintains a technical standard, a wiki and a toolset....
.) - Semantics encodingSemantics encodingA semantics encoding is a translation between formal languages. For programmers, the most familiar form of encoding is the compilation of a programming language into machine code or byte-code. Conversion between document formats are also forms of encoding. Compilation of TeX or LaTeX documents to...
of formal language A in formal language B is a method of representing all terms (e.g. programs or descriptions) of language A using language B. - Electronic encodingEncoderAn encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...
transforms a signal into a code optimized for transmissionTransmission (telecommunications)Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
or storageData storage devicethumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....
, generally done with a codecCodecA codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...
. - Neural encoding is the way in which information is represented in neurons.
- Memory encodingEncoding (Memory)Memory has the ability to encode, store and recall information. Memories give an organism the capability to learn and adapt from previous experiences as well as build relationships. Encoding allows the perceived item of use or interest to be converted into a construct that can be stored within the...
is the process of converting sensations into memories. - Television encoding: NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
, PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
Other examples of decoding include:
- Digital-to-analog converterDigital-to-analog converterIn electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
, the use of analog circuit for decoding operations - Decoding (Computer Science)ParsingIn computer science and linguistics, parsing, or, more formally, syntactic analysis, is the process of analyzing a text, made of a sequence of tokens , to determine its grammatical structure with respect to a given formal grammar...
- Decoding methodsDecoding methodsIn communication theory and coding theory, decoding is the process of translating received messages into codewords of a given code. There have been many common methods of mapping messages to codewords...
, methods in communication theory for decoding codewords sent over a noisy channel - Digital signal processingDigital signal processingDigital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
, the study of signals in a digital representation and the processing methods of these signals - Word decodingPhonicsPhonics refers to a method for teaching speakers of English to read and write that language. Phonics involves teaching how to connect the sounds of spoken English with letters or groups of letters and teaching them to blend the sounds of letters together to produce approximate pronunciations...
, the use of phonicsPhonicsPhonics refers to a method for teaching speakers of English to read and write that language. Phonics involves teaching how to connect the sounds of spoken English with letters or groups of letters and teaching them to blend the sounds of letters together to produce approximate pronunciations...
to decipher print patterns and translate them into the sounds of language
Codes and acronyms
Acronyms and abbreviations can be considered codes, and in a sense all languageLanguage
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...
s and writing systems are codes for human thought.
International Air Transport Association airport codes are three-letter codes used to designate airports and used for bag tag
Bag tag
Bag tags, also known as baggage tags, baggage checks or luggage tickets, have traditionally been used by bus, train and airline companies to route passenger luggage that is checked on to the final destination...
s.
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
Journalism
Journalism is the practice of investigation and reporting of events, issues and trends to a broad audience in a timely fashion. Though there are many variations of journalism, the ideal is to inform the intended audience. Along with covering organizations and institutions such as government and...
to mean "end of story", and it is sometimes used in other contexts to signify "the end".
See also
- Asemic writingAsemic writingAsemic writing is a wordless open semantic form of writing. The word asemic means "having no specific semantic content". With the nonspecificity of asemic writing there comes a vacuum of meaning which is left for the reader to fill in and interpret. All of this is similar to the way one would...
- Equipment codesEquipment codesAn equipment code describes the communication , navigation , approach aids and surveillance transponder equipment on board an aircraft...
- SemioticsSemioticsSemiotics, also called semiotic studies or semiology, is the study of signs and sign processes , indication, designation, likeness, analogy, metaphor, symbolism, signification, and communication...
- Quantum error correctionQuantum error correctionQuantum error correction is used in quantum computing to protect quantum information from errors due to decoherence and other quantum noise. Quantum error correction is essential if one is to achieve fault-tolerant quantum computation that can deal not only with noise on stored quantum...