December 1998
DB212: DATABASE MANAGEMENT SYSTEMS

QUESTION 1 (Compulsory)

Total Marks: 20 Marks

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Solutions and allocated marks are indicated in green.
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(a) What are the differences between a centralized database, a distributed database and a client-server database? [6]
Centralized database: all data located at a single site (1 mark), users at remote sites can generally access the database using data communication facilities (1 mark).

Distributed database: single logical database (1 mark), which is spread physically across computers in multiple locations (1 mark).

Client-server database: used to support work-group computing, e.g., decision support and other applications for a team (1 mark); designed for the distribution of work over a computer network, where many clients may share the services of a single server (1 mark).

 

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(b) What are the three important characteristics of the database approach?

The three important characteristics are:

 [3]
  • program-data independence
 [1]
  • support for multiple user-views
 [1]
  • use of a catalogue to store the database description

 

 [1]
(c) What do you understand by [6]
(i) the DBMS engine and
DBMS: This is the central component of a DBMS (1 mark) which provides access to the repository and the database (1 mark) and coordinates all of the other functional elements of the DBMS (1 mark).

 

 [3]
(ii) the Interface Subsystem
Interface Subsystem: provides facilities for users and applications to access the various components of the DBMS (1 mark): e.g., the data definition language (1 mark) and the DBMS programming language (1 mark).

 

 [3]
(d) What is the domain? Your answer should include an appropriate example. [3]
Domain: a pool of values (1 mark), from which one or more attributes draw their actual values (1 mark), e.g., domain of supplier numbers is the set of all possible supplier numbers (1 mark for any suitable example).

 

 [3]
(e) Differentiate between a unary and a ternary relationship [2]
Unary relationship: relationship between the instances of one entity type (1 mark).
Ternary relationship: a simultaneous relationship between instances of three entity types (1 mark).		 [2]