Communication and information theory was first formulated in telegraph and telephone engineering, which makes it natural that its benefits were first exploited by engineers in this field. Both areas are closely interlinked as the identification of information separated from its context is not possible. It is only idenftifiable as part of a communication situation with transmitter and receiver.
To communicate is to bridge a distance which sometimes can be very short or sometimes very long. When, where and how this distance should most efficiently be bridged over is considered by communication theory. In this matter it is mainly concerned with the process by which messages can be coded, transmitted, and decoded.
It should be noted that the theory is completely general and affects all kinds of transmitters and receivers as parts of biological, mechanical or electronic systems. It thus concerns communication between living organisms (including plants), between organisms and machines or between machines. Such communication does not assume the existence of a (spoken) language, neither awareness about the ongoing process, nor conscious established understanding. The communication can be used in a one to one, one to many, many to one, or many to many situation.
The most common application of communication theory involves the conveyance of information in the form of acoustic or visual messages. In human communication the only function of such messages is to convey meaning. When communication involves machines, the function is to command or control a process or to store and retrieve information. From a more technical point of view, communication theory is mainly concerned with the processes by which messages can be:
When telecommunication engineers thought of their devices as something which could exist in any one of a certain number of possible states and a message as something as chosen from a finite repertoire, information theory was born. Calculations of how much information the channel could carry per minute and how much was occupied by the specific message were done routinely. In this way it was meaningful to speak in terms of the informational effiency of, for example, a telephone channel and to compare it with rival coding systems. The indistinct and qualitative concept of information was here transformed into something precise and quantitative.
Of the many fields which benefit from information theory, we will mention only a few here. Physiology, especially interpreted in terms of GLS theory with its basic concepts of matter/energy and information, is strongly dependent on information theory. Calculations of how much information a special nerve fibre will carry per second, or how much information is processed per second in a certain part of the retina, are typical questions for information theory. The basic proposition here is that organisms are information systems.
Cryptography is another area which concerns the possibility to hide the existence of a message, to make a message uninteresting (trivialization, irrelevance, innocence) and to make a message inaccessible. Linguistics, particularly that subarea engaged in synthetic speech research and the voice control of computer systems, rely heavily on information theory. The fact that physicists are massively involved with information theory will be demonstrated in the section of this chapter on information physics. Semiotics, the theory of the phenomenon by which something acts as a sign to a living organism is quite naturally closely related to information theory. Also, infology, the science of presentation and reading of verbal and visual information is again naturally related to information theory.
The nearest application of information theory is, however, in information science. This area, with its strong interdisciplinary nature, is mainly devoted to structure and properties regarding information and communication in connection with theories and methods for acquisition, transmission, storing, retrieval, evaluation, distribution of information and general requirements of knowledge. This area also includes information systems, networks, functions, processes and activities conveying knowledge from a source to a user. As such it has also to examine problems of the information rich and information poor, information policies, copyrights and personal information integrity. The following areas are also considered within the sphere of information science namely: automata theory, logistics, classification theory, document retrieval theory, economic theory, and behavioural theory.
Source: Skyttner Lars (2006), General Systems Theory: Problems, Perspectives, Practice, Wspc, 2nd Edition.