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In database design, a lossless join decomposition is a decomposition of a relation into relations , such that a natural join of the two smaller relations yields back the original relation. This is central in removing redundancy safely from databases while preserving the original data. [ 1 ]
Database normalization is the process of structuring a relational database accordance with a series of so-called normal forms in order to reduce data redundancy and improve data integrity.
A decomposition of R into (X, Y) and (X, R − Y) is a lossless-join decomposition if and only if X Y holds in R. Every FD ( functional dependency ) is an MVD (multivalued dependency) because if X → {\displaystyle \rightarrow } Y, then swapping Y's between tuples that agree on X doesn't create new tuples.
In database normalization, unnormalized form (UNF or 0NF), also known as an unnormalized relation or non-first normal form (N1NF or NF 2), [1] is a database data model (organization of data in a database) which does not meet any of the conditions of database normalization defined by the relational model.
Decomposition of 1NF into 2NF [ edit ] To make a 1NF relation a 2NF relation, remove the functionally dependent attributes in the partial dependencies of the first normal form relation, and place those partial dependency dependent attributes in a relation where their corresponding determinant attributes are an entire candidate key.
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:
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.
The chase is a simple fixed-point algorithm testing and enforcing implication of data dependencies in database systems.It plays important roles in database theory as well as in practice.