The nature of information
What is information? We have already asserted that it is a profound, primitive (i.e. irreducible) concept. Dictionary definitions include “(desired) items of knowledge.” For example, one wishes to know the length of a piece of wood. It appears to be less than a foot long, so we measure it with our desktop ruler marked off in inches, with the result, let us say, “between six and seven inches.” This result is clearly an item of desired knowledge, hence information. We shall return to this example later. Another definition is “fact(s) learned about something,” implying that there is a definable object to which the facts are related, suggesting the need for context and meaning. A further definition is “what is conveyed or represented by a particular arrangement of things”; the dots on the head of a matrix printer shape a letter, the bar code on an item of merchandise represents facts about the nature, origin and price of the merchandise, and a sequence of letters can convey a possibly infinite range of meanings. A thesaurus gives as synonyms “advice, data, instruction, message, news, report.” Finally we have “a mathematical quantity expressing the probability of occurrence of a specific sequence of symbols or impulses etc. as aganst that of other sequences (i.e. messages).” This definition links the quantification of information to a probability, which, as we shall see, plays a major rôle in the development of the subject.
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