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UGC NET CSE | June 2013 | Part 2 | Question: 14

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If $D_1, D_2, \dots D_n$ are domains in a relational model, then the relation is a table, which is a subset of

  1. $D_1+D_2+ \dots +D_n$
  2. $D_1 \times D_2 \times  \dots \times D_n$
  3. $D_1 \cup D_2 \cup \dots \cup D_n$
  4. $D_1-D_2- \dots -D_n$
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2 Answers

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Ans is B

Mathematical Relations

 Given sets D1, D2, …, Dn, not necessarily distinct.

 The Cartesian product D1xD2x…xDn is the set of all (ordered) n-tuples such that d1∈D1, d2 ∈ D2, …, dn ∈ Dn

 A mathematical relation on D1, D2, …, Dn is a subset of the Cartesian product D1xD2x…xDn. ƒ D1, D2, …, Dn are the domains of  the relation. 

 n is the degree of the relation. 

The number of n-tuples in a given relation is the cardinality of that relation; the cardinality of a relation is always finite.

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