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in information theory, something conveying information. Information theory is interested only in the quantitative aspect of the information contained in a message.
The concept of a message in information theory has an essentially probabilistic character. Each source of information, or message source, can be specified by listing the possible messages and their corresponding probabilities. Suppose x1, x2, . . . . , xn are the possible messages and p1, p2, . . . . , pn are the corresponding probabilities. The information content of message xi is then taken as equal to - log2pi. An important quantity characterizing a source is the source’s entropy, which is the average information content of the messages from the source. The entropy is thus equal to
It is the magnitude of the entropy that governs the possibility of transmitting and storing the messages produced by the source.
As an example, let us consider a message source that consists of A’ successive measurements of a physical quantity that is uniformly distributed over the interval from 0 to 1. Furthermore, suppose the measurements are accurate to the nearest 0.1. The possible results of the individual measurements can then be regarded as the numbers 0.1, 0.2, . . . , 0.9. The probability of the occurrence of each number is 0.1. The messages in this example are represented by N-term sequences of digits. The probability of each message is (0.1)N. The information content of each message and the entropy of the source are equal to N log210 = 3.32A7 binary digits. The message source in this example can be said to be a random sequence of decimal digits of length N. The message sources considered in information theory are of such a form—random sequences of symbols—or, more generally, the form of stochastic processes.
When specific types of messages are studied, such as written texts, telephone signals, telegraph signals, or television signals, an approximate probabilistic model is constructed for the message source. For example, a complex Markov chain can be used for written Russian with sufficient accuracy for the purposes of information theory. Stationary stochastic processes are used as models for continuous messages. The construction of such models is based on extensive statistical data pertaining to the processes under consideration.
IU. V. PROKHOROV
message(1) (noun) Any data transmitted over a network. Just as a program becomes a "job" when it runs in the computer, data becomes a "message" when it is transmitted. See communications protocol, email, text messaging and instant messaging.
(2) (verb) To send a message. For example, "message me" means send me a text or instant message. See text messaging and instant messaging.
(3) In object technology, communicating between objects, similar to a function call in traditional programming.