Code

A code or code that German pronunciation [ ko ː t], is a mapping rule that uniquely assigns each character of a character set ( prototype quantity) a character or a string from a possibly other character set ( image set ). For example, the Morse Code establishes a relationship between letters and a sequence of short and long sounds ( and vice versa).

In communication science refers to a code in the broadest sense a language. All communication is based on the exchange of information, which are generated by the transmitter after a particular code and the receiver interprets according to the same code.

Electronically transmitted or stored data for example consist of a long series of zeros and ones (bits ), their combination as numerals, characters and / or letters (such as '11000001 '=' A ') are fixed. In another code the same bit combination could mean, for example, the number 193. For other types of data, such as measured values ​​or the nucleic bases in DNA strands is defined in codes which forms mean something.

In the coding theory is known as the elements which make up a code, " code words " the symbols that make up the code words form a "alphabet".

General meaning

In general, a code is an agreement on a set ( a set) of characters such as Index, icons or symbols ( signifiers, or references ) for the purpose of sharing information. Information does not exist in " pure" form; it is always formulated in any way. A code is - generally speaking - a formulation of information in the subject the characters syntactic, semantic and pragmatic rules. This requires the following elements ahead:

Human speech, animal sounds, but also the semiochemical molecules in bacteria and plants Communications Communications ( auxin ) are codes of varying complexity and capacity. In the case of animal sounds, bacterial, fungal and plant communication is the "agreement" created by natural evolution.

Definition

A code on the alphabets and is an injective mapping ( encoding = )

The symbols of the alphabet are not empty words over the alphabet assigns. The elements of the image set are called code words of the code. As an extension of a code refers to the mapping defined by

With a word over the alphabet is. A code is called immediately decipherable if no code word occurs as the initial portion of another code word with him. His name is clearly decipherable if its extension is injective. Everyone immediately decipherable code is uniquely decipherable, but there are also uniquely decipherable codes that are not immediately decipherable.

Efficiency

In the more specific, common meaning, a code is an agreement on a set of symbols ( references ) between Datalogging (transmitters) and readers ( receivers ) in order to establish an efficient mediation way for frequent messages. It serves the low-effort ( energy-and time -efficient ) and safe, reliable recording and transmission of information. This is done differently depending on the type of information and the application. Efficiency is obtained by reducing the complexity, whereby the capacity of the code decreases. To this end, instead of the information in its present form simpler elements and combinations of these used. These combinations refer to the original information. The more often a little is used, the lower the cost of processing an item should be.

Codes involve two aspects of efficiency:

• On one hand, they replace the original by a pure reference to this ( the signified is replaced by the code word ) and therefore only need to stock up on references, the recognizability and distinguishability guaranteed ( inerrancy ).
• Second, they mostly use a modular system by frequent references are provided by short ( wenigelementige ) combinations and rarer references by longer ( multi-element ) combinations. Thus, the simplest elements ( components, characters) can be used as often as possible and reused ( namely in almost all references ).

In a larger context, codes - regardless of their own sophistication - really efficient only through the repeated use as a tool for transmitting information. For the clarity to read system assumes in this preparatory any organization (eg learning). Codes are therefore an integral part of culture systems (for example, language, technical standards ) and develop a certain perseverance against changes. The energy minimization makes codes attractive for the transmission of information under special conditions: long-distance, large periods of time, large number of recipients, transfer with minimal effort in emergency situations, transmission by means of other systems which operate in this energy and structural dynamic range.

The efficiency can be increased by:

• The use of references in other areas, such as simulation.
• Several consecutive references. Over a long chain can also be achieved indirectly an effect.
• The use of a modular system, if this means the use of simple elements frequently is encouraged.

Niklas Luhmann uses the technical term code to refer to standardized differences ( orientational difference ).

In communication engineering is called the source code.

Redundancy

A code can be constructed so that the result in which it encodes an information containing unnecessary, so redundant components. That is, the generated sequence of symbols contains data that does not lead to the goal and if you decoded incorrectly, result in a contradictory result.

In the simplest case, the same is repeated once more. But any increased predictability of characters is redundancy: Thus, for example, the u after q in written German all redundant because a q u always follows. It would go so no information is lost, when all would be removed on a q following u. The redundancy helps one but to be able to important information despite a partial loss of data even decipher and use. So protects you against loss of information. It also allows to detect falsified information as such.

In communication engineering is referred to as the channel coding.

Examples of codes

• In biology, the genetic code is a rule according to which the information of the DNA / RNA are translated into amino acid sequences during protein
• In society, language and writing are to be regarded as code systems; see also Bernstein hypothesis In the language itself, in turn, a code is a feature of verbal communication; in the ( sociolinguistics ) the sociolect

Error detecting codes

• The International Standard Book Number ISBN uniquely identifies books and represents an error-detecting code
• The International Standard Serial Number ISSN is a unique identifier of periodicals and serials; it also represents a error-detecting code
• EAN as an error-detecting code

Secret codes

• With monoalphabetic encryption letters are replaced by other letters. Even more complex encryption method are colloquially often referred to as a code or secret code.

Computer science

• The computer is used, among other things, the ASCII (American Standard Code for Information Interchange ) to represent letters, numbers and punctuation marks by bit sequences - a so-called binary code. The Unicode Standard now covers almost all sign systems in the world.
• When programming, the programmer translates the requirements to algorithms in a source text, which is formulated according to the syntax of a particular programming language and is translated in the train of the future development of a computer program in other forms of program code - like intermediate code (eg bytecode ). The final resulting machine code contains the machine instructions that a processor can execute.
• In data transmission we used line codes
• On the Internet we find the geekcode in emails or in the Usenet