Project ForgeConsider an Entity-Relationship (ER) model in which entity sets E1 and E2 are connected by an m:n relationship R12. E1 and E3 are connected by a 1:n (1 on the side of E1 and n on the side of E3) relationship R13. E1 has two single-valued attributes a11 and a12 of which a11 is the key attribute. E2 has two single-valued attributes a21 and a22 of which a21 is the key attribute. E3 has two single-valued attributes a31 and a32 of which a31 is the key attribute. The relationships do not have any attributes. If a relational model is derived from the above ER model, then the minimum number of relations that would be generated if all the relations are in 3NF is ____.
Explanation
E1, E2, E3 each need their own relation (3 relations). The m:n relationship R12 MUST become its own separate relation (with a11, a21 as a composite key) — m:n relationships can never be merged into either participating entity's relation without violating normal form. The 1:n relationship R13 CAN be merged into E3's relation (the 'n' side) as a foreign key a11, since 1:n relationships don't need a separate relation. Total minimum: E1, E2, E3(with R13 merged in), R12 = 4 relations.
Source: GATE CS 2015 (Session 1 / 7th Feb Shift 1) (2015)
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