Definition:Relational Structure

Definition
A relational structure is an ordered pair $\struct {S, \RR}$, where:
 * $S$ is a set
 * $\RR$ is an endorelation on $S$.

Also known as
A relational structure may also be called a relational system.

Remarks
In the context of class-set theory, it is common to abuse notation by writing $\struct {C, \RR}$ when $C$ is a class and $\RR$ is a relation on $C$, and to call this a relational structure.

One must take care, as such a relational structure is not actually an ordered pair, or even, in most theories, a mathematical object of any kind, but only notational shorthand for a concept.