Three main paradigms of database

Source: Internet
Author: User

1. First paradigm: Each item in a database table is an indivisible basic data item.

2. Second paradigm: On the basis of the first paradigm, the non-primary attribute is completely dependent on the primary key.

Note: part of the function depends on: set X, Y is the two attribute set of the relationship R, there is x→y, if X ' is a true subset of x, there is X ' →y, then the Y function is called X.

Full function Dependency: set X, Y is the two set of properties of the relationship R, and × ' is a true subset of X, exists x→y, but has X '!→y for each x ', then the Y full function depends on X.

3. The third paradigm: on the basis of the second paradigm, the elimination of the transfer function dependency is that the non-primary attribute does not depend on other non-principal properties.

4.BC paradigm: On the basis of the third paradigm, each attribute is independent of other non-primary attributes.

Three main paradigms of database

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