2003年 5月16日 | CODD'S NOTATION FOR NORMALIZING DATA | BACK >> 目次 |

● Codd's notation for normalizing data □ Codd's notation for normalizing data, in which the normalization process are described briefly in 3 steps--the first normalization, the second and the third: (1) In the first normalization, the following two tasks can be completed,
- The primary key shall be identified in a file (table). (2) In the second normalization, the following task, "functional dependence" verification, can be compeleted, In "aRb" of a relation, the attribute "b" is funcitonally dependent on the attribute "a" if and when each value in "a" has no more than one value in "b."
Example-1; (3) In the third normalization, the following two tasks, "transitive dependence" verification and "derivation" elimination, can be completed, In "transitive dependence" verification, take it that "a", "b" and "c" are 3 attributes of relation R, and if "c" is functionally dependent on "b" and "b" is on "a", then "c" is on "a", and if the converses are NOT true, i.e. if "a" is not funcitonally dependent on "b" or "b" is not on "c", then "c" is said to be "transitively dependent" on "a." If (a ⇒ b ∧ b ⇒ c) is observed in｛a, b, c｝on the assumption that "a" is the primary key, then (c ⇒ a) can be, "c" is transitively dependent on "a".
The transitive dependence shall be removed by splitting the relation into two:
Example-2; - All the deprivations shall be removed from a file (table),
Example-3; |

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