Normal form

Normal form

The term normal form is used in a variety of contexts. Many of the uses in mathematics are special cases of a single situation, looked at abstractly: within an equivalence class one specifies a representative element, which is in a simplest or most manageable or otherwise tidiest and most desirable form, in terms of structure or syntax. A little more loosely, an equivalence class might contain several examples of such special, distinguished elements. For example, the Jordan normal form under similarity of matrices (link below) may mean any suitable block matrix in similarity class, and in the general case there can be several such.

In Boolean algebra:

conjunctive normal form
disjunctive normal form

In relational database theory

first normal form
second normal form
third normal form
fourth normal form

see Database normalization for all four.

In linear algebra:

Jordan normal form

In musical set theory:

the normal form of a pitch or pitch class set.

To transform something into a normal form is often called normalization.