Let R (ABCDE) be a relation schema and consider the following functional dependencies F = { AB→ E, AD→B, B→ C, C →D}. Find out the candidate key.
Case 1: as B→C and C →D, so B→D (transitivity)
as B→D so AB→AD (augmentation)
as AB→E so AB→ABE (reflexivity)
as AB→ABE, AND AB→AD so AB→ABCDE(union)
So the closure of AB is . so, AB is a candidate key.
Case 2: as AD→B so AD→ABD (reflexivity)
as AB→E so ABD→DE (augmentation)
as AD→B and B→C so ADrarr;C (transitivity)
as AD→ABD, AD→C and AD→DE so AD→ABCDE (union)
So the closure of AB is 
. so, AD is also a candidate key.
Describe the Three-Schema Architecture of DBMS. Distinguish Physical Data Independence and Logical Independence.
Write the characteristics of a good user interface.
Define software quality. Briefly explain McCall’s quality factors.
