1.Consider a relation R with ?ve attributes ABCDE. You are given the following dependencies: A → B, BC → E, and ED → A. 

1. List all keys for R.

2. Is R in 3NF?

3. Is R in BCNF?

2.Assume that you are given a relation with attributes ABCD. 

1. Assume that no record has NULL values. Write an SQL query that checks whether the functional dependency A → B holds. 

2. Assume again that no record has NULL values. Write an SQL assertion that enforces the functional dependency A → B. 

3. Let us now assume that records could have NULL values. Repeat the previous two questions under this assumption.

3.Suppose that we have the following three tuples in a legal instance of a relation schema S with three attributes ABC (listed in order): (1,2,3), (4,2,3), and (5,3,3). 

1. Which of the following dependencies can you infer does not hold over schema S? 

(a) A → B, (b) BC → A, (c) B → C 

2. Can you identify any dependencies that hold over S?

4.Answer the following questions brie?y:

1. Explain how media recovery is handled in ARIES. 

2. What are the pros and cons of using fuzzy dumps for media recovery? 

3. What are the similarities and di?erences between checkpoints and fuzzy dumps? 

4. Contrast ARIES with other WAL-based recovery schemes. 

5. Contrast ARIES with shadow-page-based recovery.

5.Consider the three conditions under which a redo is unnecessary (Sec-tion 18.6.2). 

1. Why is it cheaper to test the ?rst two conditions?

2. Describe an execution that illustrates the use of the ?rst condition. 

3. Describe an execution that illustrates the use of the second condition.