Reference no: EM133300697

Questions

1. Discuss attribute semantics as an informal measure of goodness for a relation schema.

2. Discuss insertion, deletion, and modification anomalies. Why are they considered bad? Illustrate with examples.

3. Why should NULLs in a relation be avoided as much as possible? Discuss the problem of spurious tuples and how we may prevent it.

4. State the informal guidelines for relation schema design that we discussed. Illustrate how violation of these guidelines may be harmful.

5. What is a functional dependency? What are the possible sources of the information that defines the functional dependencies that hold among the attributes of a relation schema?

6. Why can we not infer a functional dependency automatically from a particular relation state? Exercises 497

7. What does the term unnormalized relation refer to? How did the normal forms develop historically from first normal form up to Boyce-Codd normal form?

8. Define first, second, and third normal forms when only primary keys are considered. How do the general definitions of 2NF and 3NF, which consider all keys of a relation, differ from those that consider only primary keys?

9. What undesirable dependencies are avoided when a relation is in 2NF?

10. What undesirable dependencies are avoided when a relation is in 3NF?

11. In what way do the generalized definitions of 2NF and 3NF extend the definitions beyond primary keys?

12. Define Boyce-Codd normal form. How does it differ from 3NF? Why is it considered a stronger form of 3NF?

13. What is multivalued dependency? When does it arise?

14. Does a relation with two or more columns always have an MVD? Show with an example.

15. Define fourth normal form. When is it violated? When is it typically applicable?

16. Define join dependency and fifth normal form.

17. Why is 5NF also called project-join normal form (PJNF)?

18. Why do practical database designs typically aim for BCNF and not aim for higher normal forms?