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 (A₁,A₂,..........A_N), also denoted by r(R) is a set of n-tuples

r = {t₁,t₂,............t_m}

Where each n-tuple is an ordered list of n values

t  =  1,v₂,........, 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'.