GATE | GATE-CS-2009 | Question 56

Consider the following relational schema:

Suppliers(sid:integer, sname:string, city:string, street:string)
Parts(pid:integer, pname:string, color:string)
Catalog(sid:integer, pid:integer, cost:real)

Assume that, in the suppliers relation above, each supplier and each street within a city has a unique name, and (sname, city) forms a candidate key. No other functional dependencies are implied other than those implied by primary and candidate keys. Which one of the following is TRUE about the above schema?
(A) The schema is in BCNF
(B) The schema is in 3NF but not in BCNF
(C) The schema is in 2NF but not in 3NF
(D) The schema is not in 2NF

Answer: (A)

Explanation: A relation is in BCNF if for every one of its dependencies X → Y, at least one of the following conditions hold:

    X → Y is a trivial functional dependency (Y ⊆ X)
    X is a superkey for schema R 

Since (sname, city) forms a candidate key, there is no non-tirvial dependency X → Y where X is not a superkey

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