DBMS

31. Explain the two types of participation constraint.

• Total: The participation of an entity set E in a relationship set R is said to be total if every

entity in E participates in at least one relationship in R.

• Partial: if only some entities in E participate in relationships in R, the participation of entity set

E in relationship R is said to be partial.

32. What is meant by lossless-join decomposition? APRIL/MAY-2011

We claim the above decomposition is lossless. How can we decide whether decomposition is

lossless?

1. Let R be a relation schema.

2. Let F be a set of functional dependencies on R.

3. Let R1and R2 form a decomposition of R.

4. The decomposition is a lossless-join decomposition of R if at least one of the following functional dependencies are in :

a. R1∩ R2→ R1

b. R1∩ R2→ R2

33. List the disadvantages of relational database system

Repetition of data

Inability to represent certain information.

34. What is first normal form?

The domain of attribute must include only atomic (simple, indivisible) values.

35. What is meant by functional dependencies?

Consider a relation schema R and a C R and ß C R. The functional dependency a ß holds on

relational schema R if in any legal relation r(R), for all pairs of tuples t1 and t2 in r such that t1 [a] =t1 [a], and also t1 [ß] =t2 [ß].

36. What are the uses of functional dependencies?

To test relations to see whether they are legal under a given set of functional dependencie s. To specify constraints on the set of legal relations.

37. Explain trivial dependency?

Functional dependency of the form a ß is trivial if ß C a. Trivial functional dependencies are satisfied by all the relations.

38. What are axioms?

Axioms or rules of inference provide a simpler technique for reasoning about functional dependencies.

39. What is meant by computing the closure of a set of functional dependency?

+ The closure of F denoted b y F is the set of functional dependencies logically implied by F.

40. What is meant by normalization of data?

It is a process of analyzing the given relation schemas based on their Functional Dependencies

(FDs) and primary key to achieve the properties

Ø Minimizing redundancy

Ø Minimizing insertion, deletion and updating anomalies

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