Définition de «projection»

projection: La projection d'une relation X(A1,...,An) sur les attributs Ai,...,Aj(1≤i,j≤n et i différent de j) est la relation X(Ai,...,Aj) pour laquelle les tulpes doublons sont éliminés.
Cet opérateur ne porte que sur 1 relation.
Il permet de ne retenir que certains attributs spécifiés d'une relation.
On obtient tous les n-tulpes de la relation à l'exception des doublons.

Catégories

Mathématique

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Document created the 19/03/2002, last modified the 15/12/2024
Source of the printed document:https://www.gaudry.be/en/glossaire/projection

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