August 1999
DB212 : DATABASE MANAGEMENT SYSTEMS

QUESTION 1 (Compulsory)

Total Marks: 20 Marks

 Click here to access other questions

 

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
Return to Question 1
(a) (i) What is multi-valued attribute?

(ii) Give an example of a simple E-R diagram to show how a multi-valued attribute would be represented. Explain how this representation would be changed by normalization.

 [1]

[3]
(i)
Multivalued Attribute: an attribute that have more than one value for each entity instance

 
(ii)
Multi-valued attribute representation.

pic1.gif (6359 bytes)

 

Normalization representation

pic2.gif (5401 bytes)

 
(b) Give four reasons why normalization is carried out. [4]
Reasons for normalization:
  • The databases design must be efficient (performance-wise)
  • The amount of data should be reduced if possible
  • The design should be free of update, insertion and deletion anomalies
  • The design must comply with rules regarding relational databases
  • The design has to show pertinent relationships between entities
  • The design should permit simple retrieval and simple data maintenance, and should reduce the need to restructure data

 
(c) Identify four models used in database modelling. [4]
Four models used in Database Modelling:
  • Object-Orientated Data Model
  • Hierarchical Data Model
  • Network Data Model
  • Relational Data Model

 
(d) What is meant by concurrency control? [2]
Concurrency control : prevent of the loss of data integrity (1 mark) due to interference between users in a multi-user envionrment (1 mark).

 
(e) State the Entity Integrity Rule. [2]
Entity Integrity Rule : no component of the primary key of a relation can be given null values.

 
(f) List four operations that can be executed by the Data Definition Language (DDL) component of the Structured Query Language (SQL). [4]
Possible Data Definition Language (DDL) operations are:
  • Create Tables
  • Modify Tables (ALTER)
  • Create Indexes
  • Drop Tables
  • Drop Indexes
  • Authorization (GRANT)
  • Reauthorization (REVOKE)