Two marks Questions with Answers

Two Marks Questions with Answers

Q.1 Define distributed database management system.  AU: May-08,18, Dec.-16

Ans.: A distributed database system consists of loosely coupled sites (computer) that share no physical components and each site is associated a database system.

Q.2 What are two approaches to store a relation in the distributed database? AU: May-04

 Ans.: (1) Replication: System maintains multiple copies of data, stored in different sites, for faster retrieval and fault tolerance.

(2) Fragmentation: Relation is partitioned into several fragments stored in distinct sites.

Q.3 What are various fragmentations? State various fragmentations with example. AU: Dec.-17

Ans.: There are two types of fragmentations - Horizontal fragmentation and vertical fragmentation.

Example - Refer section 5.1.3.2.

   • Horizontal fragmentation: In this approach, each tuple of r is assigned to one or more fragments. If relation R is fragmented in r1 and r2 fragments, then to bring these fragments back to R we must use union operation. That means R=r1ur2

   • Vertical fragmentation: In this approach, the relation r is fragmented based on one or more columns. If relation R is fragmented into r1 and r2 fragments using vertical fragmentation then to bring these fragments back to original relation R we must use join operation. That means R= r1 r2

Q.4 What are the advantages of distributed databases?

Ans.:

(1) There is fast data processing as several sites participate in request processing.

(2) Reliability and availability of this system is high.

(3) It possess reduced operating cost.

(4) It is easier to expand the system by adding more sites.

(5) It has improved sharing ability and local autonomy.

Q.4 List out the reasons for development of distributed databases.

Ans.: Following are the reasons for development of distributed databases –

(1) To control the data present at geographically different sites.

(2) To obtain highly available and reliable data processing systems.

Q.5 Difference between homogeneous and heterogeneous schema.

Ans. :

Q.6 What are the advantages of fragmentation?

Ans.: (1) It allows parallel processing on fragments of a relation.

(2) It allows a relation to be split so that tuples are located where they are most frequently accessed.

Q.7 Give an example of two phase commit protocol. AU: Dec.-15

Ans.: Refer section 5.1.4.3.

• The atomicity is an important property of any transaction processing. What is this atomicity property? This property means either the transaction will execute completely or it won't execute at all.

• The commit protocol ensures the atomicity across the sites in following ways -

i) A transaction which executes at multiple sites must either be committed at all the sites, or aborted at all the sites.

ii) Not acceptable to have a transaction committed at one site and aborted at another.

• There are two types of important sites involving in this protocol -

   • One Coordinating site

   • One or more participating sites.