A relation instance indicates as r is a collection of tuples for a given relational schema at a exact point of time.
A relation state r of the relation schema R (A_{1},A_{2},..........A_{N}), also denoted by r(R) is a set of n-tuples
r = {t_{1},t_{2},............t_{m}}
Where each n-tuple is an ordered list of n values
t = 1,v_{2},........, v_{n}>
where every v_{i} belongs to domain (Ai) or includes null values.
The relation schema is also known as 'intension' and relation state is also known as 'Extension'.