Relational model
The relational model is a manner of modelling the contained informations in Database which rests on mathematical principles invented by E.F. Codd. What is called relation is a whole of attributes which define a fact - for example that an employee has a given number, that its name is so-and-so, that he works in such service and was engaged on such date. Each authority is called a tuple. The relations are usually represented in tabular form, and one confuses table and relation; one confuses in the same way, line in the table and tuple. By definition, each tuple of a relation is single, and is identified by one or a combination of several attributes which forms the key. The order of the tuples is nonsignificant.
Codd defined a relational algebra and operators, who allow to obtain other relations starting from relations. The ideas of Codd were implemented, and passably perverted, in the relational databases or SGBDR such as the experimental project System/R, then commercial products such as Oracle, DB2 or MySQL, and in the language of handling of the data SQL.
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