When a new row is written to the table, a new unique value for the primary key is generated; this is the key that the system uses primarily for accessing the table. Other, more natural keys may also be identified and defined as alternate keys (AK).
A relation is thus a heading paired with a body, the heading of the relation being also the heading of each tuple in its body.
The number of attributes constituting a heading is called the degree, which term also applies to tuples and relations. Codd used the term "relation" in its mathematical sense of a finitary relation, a set of tuples on some set of n sets S Thus, an n-ary relation is interpreted, under the Closed World Assumption, as the extension of some n-adic predicate: all and only those n-tuples whose values, substituted for corresponding free variables in the predicate, yield propositions that hold true, appear in the relation.
A set of attributes in which no two distinct elements have the same name is called a heading.
A set of tuples having the same heading is called a body.
The various software systems used to maintain relational databases are known as a relational database management system (RDBMS).