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Fifth normal form (5NF), also known as projection–join normal form (PJ/NF), is a level of database normalization designed to remove redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships.
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. Informally, a relational database relation is often described as "normalized" if it meets third normal form. [7] Most 3NF relations are free of insertion, updation, and ...
The join dependency plays an important role in the fifth normal form (5NF), also known as project-join normal form, because it can be proven that if a scheme is decomposed in tables to , the decomposition will be a lossless-join decomposition if the legal relations on are restricted to a join dependency on called (,, …,).
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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.
3NF—third normal form; 386—Intel 80386 processor; 486—Intel 80486 processor; 4B5BLF—4-bit 5-bit local fiber; 4GL—fourth-generation programming language; 4NF—fourth normal form; 5GL—fifth-generation programming language; 5NF—fifth normal form; 6NF—sixth normal form; 8B10BLF—8-bit 10-bit local fiber; 802.11—wireless LAN
Denormalization is a strategy used on a previously-normalized database to increase performance. In computing, denormalization is the process of trying to improve the read performance of a database, at the expense of losing some write performance, by adding redundant copies of data or by grouping data.