relational database model

A formal model of databases proposed by E.F. Codd in 1970.

A database is a set of tables (mathematically speaking, relations). Queries on the tables can now be posed using standard mathematical logic. Tables can also be manipulated in whole, with the relational algebra.

There is no explicit notion of object in this model. But the rows (tuples) or cells (values) in the tables often represent real world objects.

This is known as the object identity problem.

In the relational database model, data can be visualized as being stored in a number of tables, where each table represents a relation. Columns in the table are attributes of each relation, while the rows in the table consist of tuples that describe each instance of the relation.

The relation schema is defined as R(A₁, A₂...A_n) where R is the name of the relation and each attribute A_i is the role a domain (for example, the set of all 9-digit integers as a domain for social security number) plays in the relation. The degree of R is the number of attributes in its schema.

An instance, or relation state of a relation, r(R) consists of a set of n-tuples r{t₁, t₂, .... , t_n}.

Tables in the relational database model are manipulated through relational algebra.