Fifth normal form

5NF
Fifth normal form (5NF), also known as project-join normal form (PJ/NF), is a level of database normalization designed to reduce redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships.wikipedia
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Database normalization

normalizationnormalizednormal form
Fifth normal form (5NF), also known as project-join normal form (PJ/NF), is a level of database normalization designed to reduce redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships.
To spot a table not satisfying the 5NF, it is usually necessary to examine the data thoroughly.

Join dependency

lossless-join decompositionrecovered by rejoining the projections
A table is said to be in the 5NF if and only if every non-trivial join dependency in that table is implied by the candidate keys.
The join dependency plays an important role in the Fifth normal form, also known as project-join normal form, because it can be proven that if a scheme R is decomposed in tables R_1 to R_n, the decomposition will be a lossless-join decomposition if the legal relations on R are restricted to a join dependency on R called.

Fourth normal form

4NF4NF database normalization
Only in rare situations does a 4NF table not conform to 5NF.
Only in rare situations does a 4NF table not conform to the higher normal form 5NF.

Semantics

semanticsemanticallymeaning
Fifth normal form (5NF), also known as project-join normal form (PJ/NF), is a level of database normalization designed to reduce redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships.

Table (database)

tabletablesdatabase table
A table is said to be in the 5NF if and only if every non-trivial join dependency in that table is implied by the candidate keys.

If and only if

iffif, and only ifmaterial equivalence
A table is said to be in the 5NF if and only if every non-trivial join dependency in that table is implied by the candidate keys. A join dependency *{A, B, … Z} on R is implied by the candidate key(s) of R if and only if each of A, B, …, Z is a superkey for R.

Candidate key

candidatekey candidateskeys
A table is said to be in the 5NF if and only if every non-trivial join dependency in that table is implied by the candidate keys.

Superkey

A join dependency *{A, B, … Z} on R is implied by the candidate key(s) of R if and only if each of A, B, …, Z is a superkey for R.

Ronald Fagin

The fifth normal form was first described by Ronald Fagin in his 1979 conference paper Normal forms and relational database operators.

Multivalued dependency

multivalued dependenciesembedded multi-valued dependencies (EMVD s)
Also note that the table is in 4NF, since there are no multivalued dependencies (2-part join dependencies) in the table: no column (which by itself is not a candidate key or a superkey) is a determinant for the other two columns.

Attribute-value system

attributeattribute valuesattribute-value centric
*Attribute-value system

Domain-key normal form

Domain/key normal formDKNFDomain Key Normal Form
The third normal form, Boyce–Codd normal form, fourth normal form and fifth normal form are special cases of the domain/key normal form.

Third normal form

3NF3NF databasesthird
Certain types of 3NF tables, rarely met with in practice, are affected by such anomalies; these are tables which either fall short of Boyce–Codd normal form (BCNF) or, if they meet BCNF, fall short of the higher normal forms 4NF or 5NF.

Han unification

UnihanUnihan DatabaseCJK Unified Ideographs
All tables in this database are in fifth normal form.