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Intro to Inference Rules

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• Introduction
  • Pre-requisite to decomposing a relation:

    In order to decompose a relation R, we must know whether a dependency a is "good" dependency or a "bad" dependency

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  • How to tell if a dependency is good or bad:

    A dependencies caused by a key is a "natural" functional dependency and it is a "good" dependency

    Therefore:

    In order to determine whether a dependency is "good" dependency or "bad" dependency: We must first find all the keys of a relation (If we don't know if some attribute is a key or not key, we cannot tell if the dependency is natural or not !!!)

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• Theory/technique on finding keys in a relation
  • The pre-requisite to performing decomposition on a relation R is:

    Finding all the keys of the relation R

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  • The theory/technique on how to find all the keys of a relation is based on:

    Inference rules

    We will therefore first study inference rules now....