Fourth normal form (4NF) is a normal form used in database normalization. Introduced by Ronald Fagin in 1977, 4NF is the next level of normalization after Boyce–Codd normal form (BCNF). Whereas the second, third, and Boyce–Codd normal forms are concerned with functional dependencies, 4NF is concerned with a more general type of dependency known as a multivalued dependency. A Table is in 4NF if and only if, for every one of its non-trivial multivalued dependencies X Y, X is a superkey—that is, X is either a candidate key or a superset thereof.
Read more about Fourth Normal Form: Multivalued Dependencies, Example, 4NF in Practice
Famous quotes containing the words fourth, normal and/or form:
“What, to the American slave, is your Fourth of July? I answer: A day that reveals to him, more than all other days in the year, the gross injustice and cruelty to which he is the constant victim. To him your celebration is a sham.”
—Frederick Douglass (c.1817–1895)
“Separation anxiety is normal part of development, but individual reactions are partly explained by experience, that is, by how frequently children have been left in the care of others.... A mother who is never apart from her young child may be saying to him or her subliminally: “You are only safe when I’m with you.””
—Cathy Rindner Tempelsman (20th century)
“Natural selection, the blind, unconscious, automatic process which Darwin discovered, and which we now know is the explanation for the existence and apparently purposeful form of all life, has no purpose in mind. It has no mind and no mind’s eye. It does not plan for the future. It has no vision, no foresight, no sight at all. If it can be said to play the role of the watchmaker in nature, it is the blind watchmaker.”
—Richard Dawkins (b. 1941)