In
relational database theory, a
relation, as originally defined by
E. F. Codd, is a set of
tuples (d
1, d
2, ..., d
n), where each element d
j is a member of D
j, a
data domain. Codd's original definition notwithstanding, and contrary to the usual definition in mathematics, there is no ordering to the elements of the tuples of a relation. Instead, each element is termed an
attribute value. An
attribute is a name paired with a domain (nowadays more commonly referred to as a
type or
data type). An
attribute value is an attribute name paired with an element of that attribute's domain, and a tuple is a
set of attribute values in which no two distinct elements have the same name. Thus, in some accounts, a tuple is described as a
function, mapping names to values.