# 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

### Sixth normal form

**6NF**

Any relation in 6NF is also in 5NF.

### 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.