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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,..........AN), also denoted by r(R) is a set of n-tuples
r = {t1,t2,............tm}
Where each n-tuple is an ordered list of n values
t = 1,v2,........, vn>
where every vi belongs to domain (Ai) or includes null values.
The relation schema is also known as 'intension' and relation state is also known as 'Extension'.
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