A more structured 3NF is called the Boyce-Codd Normal Form (BCNF). A table is in BCNF if every determinate column is a candidate key. A determinate column is one on which some of the columns are fully functional. These are tables that have composite candidate keys, multiple candidate keys, or candidate keys that overlap.A table in fourth normal form (4NF) is in BCNF and has no multi-valued dependencies. A multi-valued dependency (MVD) is when one column has values in multiple rows that match a single value in another column of the same table. Suppose an employee works at multiple stores and is a customer representative for multiple customers. If you place all of this data into a single table, you must use all three attributes as the key because only all three attributes as keys can identify a unique row. The MVD relationship between employee and store says where each employee works. The MVD relationship between employee and customer says how many customers buy products from this employee. To change a table with MVDs to 4NF, move each MVD pair to a new table.

A table in fifth normal form (5NF) is in 4NF and has no join dependencies. 5NF table’s objectives are to have tables that can not be split into smaller tables. Most tables are already in 5NF and no further effort is necessary. Most people only have to normalize to 1NF, 2NF, 3NF, and sometimes 4NF.