from patrick

Question 1

a) Define the following terms as used in databases:

i) Entity [2 marks]
ii) Tuple [2 marks]
iii) Derived attribute [2 marks]

Answer 1

i) Entity: A real-world object or concept with distinct characteristics, stored as a record in a database.

ii) Tuple: A single row in a table representing a set of related data (a record).

iii) Derived attribute: An attribute whose value is calculated from other attributes in the database.

Question 2

b) Give one example of a derived attribute [1 mark]

Answer 2

An example of a derived attribute is Age, which can be calculated from a person’s Date of Birth.

Question 3

c) With the use of examples, explain the differences between the following:
i) Simple attribute VS single valued attribute [4 marks]

Answer 3

a simple attribute is one piece of data that cant be broken down further . its indivisible. e,g First name

while

single valued attribute contains one value for each record. e.g StudentID

Question 4

c) With the use of examples, explain the differences between the following:
ii) Composite attribute VS multi-valued attribute [4 marks]

Answer 4

a composite is an attribute that can be divided into smaller parts. e.g full address can be broken int street , city , zip code

while

a multi attribute is an attribute that can have multiple values. e,g phone number can have can include home and mobile phone number.

Question 5

d) Identify and explain in brief any two symbols used in the development of ER diagrams. [4 marks]

Answer 5

Rectangle(entity) - represents real world object or concept.

diamond(relationship) - represents a relationship between entities

Question 6

with examples Explain the purposes of the following aggregate functions? [6 marks]
i. Max()
ii. Count()
iii. Avg()

Answer 6

Max() returns highest value in a column. e.g
SELECT MAX(Salary) FROM Employees

Count(). returns now of rows that match a condition e.g SELECT COUNT(*) FROM Students WHERE Course = ‘Computer Science’;

Avg() returns average value in a numeric column. SELECT AVG(Price) FROM Products;

Question 7

a) Give any three examples of DBMSs. [3 marks]

Answer 7

Oracle database
MySQL
PostgreSQL

Question 8

b) The basic data storage structure for a relational database is a relation. Give and explain any four properties of a relation. [8 marks]

Question 9

c) With the help of an illustration, explain the three-layered architecture model for database design. [6 marks]

Answer 9

Tabular Format: Data is stored in tables with rows and columns, where each table represents a relation.

Unique Rows: Each row in a table must be unique; no two rows can have the same values in all columns.

Attribute Names: Columns (attributes) in a table have unique names, and each column contains data of a specific type.

Order Independence: The order of rows and columns does not affect the data; rows can be retrieved in any sequence.

Question 10

d) Using an example, describe a unary relationship [2 marks]

Answer 10

draw

Question 11

e) Explain THREE(3) advantages of database systems over file systems (paper-based)
[6 marks]

Answer 11

Data Integrity: Databases enforce rules to maintain accuracy and consistency of data, reducing errors compared to manual paper-based systems.

Efficiency: Databases support quick data retrieval and manipulation through queries, while file systems can be slower and more cumbersome to manage.

Concurrent Access: Databases allow multiple users to access and update data simultaneously, whereas paper-based systems are limited to single-user access.

Question 12

a) Describe the five components of the DBMS environment and discuss how they relate to each other. [10 marks]

Answer 12

hard

Question 13

b) Give and explain any 5 functions a DBMS can support [5 marks]

Answer 13

Data Storage: Stores and organizes data efficiently in tables or files.

Data Retrieval: Provides tools to query and retrieve specific data from the database.

Data Manipulation: Allows users to insert, update, and delete data.

Data Security: Controls access to data through user authentication and authorization.

Backup and Recovery: Offers mechanisms to back up data and restore it in case of loss or corruption.

Question 14

c) Within the context of databases, define a data model. [2 marks]

Answer 14

Collection of logical constructs used to represent data structure and relationships within the database

Question 15

d) Give any two examples of data models. [2 marks]

Answer 15

hierarchial model. represented by an upside down tree. -adv conceptual simplicity , efficiency and data independence . cons complex implementation , lacks structural independence.

network db model. conceptual simplicty promotes db integrity.. lacks structural independence.

relational db. struectural independence, improved conceptual simplicity. dis poor design and implementation is made easy. may promote islands of info problems. Substantial hardware and system software overhead

Question 16

e) Identify and explain in brief three concerns addressed by a relational data model. [6 marks]

Answer 16

dis
poor design and implementation is made easy.
may promote islands of info problems.
Substantial hardware and system software overhead

Question 17

a) Distinguish between the Data Definition Language (DDL) and the Data Manipulation Language (DML) [2 marks]

Answer 17

ddl - statements that specify and modify db schemas e.d CREATE, Alter, DROP

while
DML - statments that manipulate db content. INSERT , UPDATE , DELETE

Question 18

c) State Two (2) advantages of a Network database model [2 marks]

Answer 18

data independence
conceptual simplicity

Question 19

e) Identify and explain in brief Three (3) concerns addressed by a relational data model. [6 marks]

Question 20

c) Give and explain any Four (4) properties of a relation. [8 marks]

Question 21

d) The student wrote a query to list the students who stay in Gaborone or Francistown as follows:

Select * from student where city = ‘Gaborone’ OR city = ‘Francistown’

Rewrite the above SQL statement using the IN operator.

Answer 21

SELECT * FROM student WHERE city IN (‘Gaborone’ , ‘Francistown’);

Question 22

e) Tshepo wanted to design a database using object oriented approach. He has asked you to differentiate between an object and a class in object oriented data model. What is the difference between these two?
[4 marks]

Answer 22

an object is an instance of a class while class is a blueprint/template of an object

a class co

Question 23

f) Identify and explain in brief any THREE objectives of the three level architecture [6 marks]

Answer 23

Consistent Data Access: All users access the same data.

View Independence: Changes in one view do not affect others.

Storage Abstraction: Users are unaware of physical data storage details.

Question 24

a) Define the following terms as used in databases:
i) Record [2 marks]
ii) Primary key [2 marks]
iii) Entity integrity [2 marks]

Answer 24

Record: A single row in a table, representing a set of related data items about an entity.

ii) Primary Key: A unique identifier for each record in a table, ensuring no duplicate rows.

iii) Entity Integrity: A constraint ensuring that the primary key of a table is unique and not null, maintaining data accuracy and consistency.

Question 25

c) Identify only one operator under the following groups and explain when each is used.
i. Comparison operator
ii. List operator
[4 marks]

Answer 25

List Operators: Used to check if a value matches any value in a list (e.g., IN, BETWEEN).

Comparison Operators: Used to compare values (e.g., =, <>, >, <, >=, <=).

Set Operators: Used to combine results from multiple queries (e.g., UNION, INTERSECT, EXCEPT).

Logical Operators: Used to combine multiple conditions (e.g., AND, OR, NOT).

Question 26

do 3a

Question 27

do 4a

Question 28

d) Using an example, describe a unary relationship [2 marks]