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Fourth normal form (4NF) is a normal form used in database normalization. Introduced by Ronald Fagin in 1977, 4NF is the next level of normalization after Boyce–Codd normal form (BCNF). Whereas the second , third , and Boyce–Codd normal forms are concerned with functional dependencies , 4NF is concerned with a more general type of ...
Codd went on to define the second normal form (2NF) and third normal form (3NF) in 1971, [5] and Codd and Raymond F. Boyce defined the Boyce–Codd normal form (BCNF) in 1974. [6] Ronald Fagin introduced the fourth normal form (4NF) in 1977 and the fifth normal form (5NF) in 1979. Christopher J. Date introduced the sixth normal form (6NF) in 2003.
In database normalization, fourth normal form requires that for every nontrivial multivalued dependency X Y, X is a superkey. A multivalued dependency X ↠ {\displaystyle \twoheadrightarrow } Y is trivial if Y is a subset of X , or if X ∪ Y {\displaystyle X\cup Y} is the whole set of attributes of the relation.
Boyce–Codd normal form (BCNF or 3.5NF) is a normal form used in database normalization. It is a slightly stricter version of the third normal form (3NF). By using BCNF, a database will remove all redundancies based on functional dependencies .
Boyce–Codd normal form (BCNF) was developed in 1974 by Boyce and Edgar F. Codd. It is a type of normal form that is used in database normalization. The goal of relational database design is to generate a set of database schemas that store information without unnecessary redundancy. Boyce-Codd accomplishes this and allows users to retrieve ...
The third normal form, Boyce–Codd normal form, fourth normal form and fifth normal form are special cases of the domain/key normal form. All have either functional, multi-valued or join dependencies that can be converted into superkeys. The domains on those normal forms were unconstrained so all domain constraints are satisfied.
The sixth normal form is currently as of 2009 being used in some data warehouses where the benefits outweigh the drawbacks, [9] for example using anchor modeling.Although using 6NF leads to an explosion of tables, modern databases can prune the tables from select queries (using a process called 'table elimination' - so that a query can be solved without even reading some of the tables that the ...
The third normal form (3NF) is a normal form used in database normalization. 3NF was originally defined by E. F. Codd in 1971. [2] Codd's definition states that a table is in 3NF if and only if both of the following conditions hold: The relation R (table) is in second normal form (2NF).