Consider 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 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 ___________.
Entity E1. a1 a12 -------- a11 is key Entity E2 a21 a22 -------- a22 is key Entity E3 a31 a32 -------- a31 is key R12 is m:n Relationship between E1 and E2 R12 a11 a22 ------------- (a11, a22) is key. R13 is 1:n Relationship between E1 and E3 R13 a11 a31 ----------- (a11, a31) is key. We need minimum no. of tables. Can we remove any of the above tables without loosing information and keeping the relations in 3NF? We can combine R13 and R12 into one. a11 a31 a22 ------------------ (a11, a31, a22) is key. The relation is still in 3NF as for every functional dependency X -> A, one of the following holds 1) X is a superkey or 2) A-X is prime attribute