7.41

Explain why 4NF is a normal form more desirable than BCNF.

---

4NF is more desirable because it removes redundancy that BCNF doesn’t.

To quote an example from the book presented on the beginning of section 7.6, take the relational schema:-

r2(ID,dept_name,street,city)

We must repeat the department name once for each address that an instructor has, and we must repeat the address for each department with which an instructor is associated. Eventhough, we have this redundancy the relation r2 is still in BCNF, though it is NOT in 4NF.

4NF removes this redundancy, by decomposing r2 into the schemas:-

(ID, dept_name)
(ID, street, city)