What are Armstrong rules? How do we say that they are complete and/or sound

 

The well-known inference rules for FDs         

Reflexive rule : 

                                      If Y is subset or equal to X then X        Y.

Augmentation rule:

                             If X       Y then XZ        YZ.

Transitive rule:

                             If  {X      Y, Y       Z} then X        Z.

Decomposition rule :

                                      If X       YZ then X     Y.

Union or Additive rule:

                                      If {X       Y, X        Z} then X             YZ.

Pseudo Transitive rule :

                                      If {X      Y, WY        Z} then WX      Z.

          Of these the first three are known as Amstrong Rules. They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules.

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RDBMS