Relation:Tutorial 2

A relation is a set of zero or more tuples that share the same properties.
The cardinality of a relation is the number of tuples. The empty relation {} or ∅ has no tuples and the cardinality 0.
A tuple is a set of zero or more property-value pairs. Each property has its domain. A domain is the set of all possible values. N (set of natural numbers) is a domain for example.
The arity is the number of properties of the tuples in a relation. The properties do not have a particular order.