Week 2

Question 1

What are the two main components of designing a database

Answer 1

Database design and application design

Question 2

What does database design entail

Answer 2

designing the conceptual schema

As well as physical and implementation schema

Question 3

What does application design focus on

DONT NEED TO NO MUCH AS IT IS CONSIDERED PART OF SOFTWARE ENGINEERING

Answer 3

focuses on the programs and interfaces that ACCESS the database

Question 4

What is the first thing you need before you can even think about designing a schema

Answer 4

A specification - The requirements the database must follow

eg:
an employee can only work for one department …

Question 5

What are the main concepts of an entity relationship model

Answer 5

.ENTITIES ( the objects)
.ATRIBUTES ( the properties of the entities)
. RELATIONSHIPS ( between 2 or more entities)

Question 6

2 types of entities

Answer 6

. physical
. Non physical

Question 7

Features of an attribute

Answer 7

.has an associated value
eg :
Name - “Abdullahi Mohamed”
ID - 1234543

. has an associated data type
Integer, double, string …

Question 8

What are the types of attributes and define them

Answer 8

Simple attribute - cannot be divided into further components (Atomic)
eg Kings_ID - k123456

composite attribute attribute - can be divided into further components

Name( FirstName_ , MiddleName_ , LastName_ )

Address (Street, postcode city)

Question 9

Employees with the same basic attributes can be grouped into an …

Answer 9

Entity type

eg employees can be grouped into entity type EMPLOYEE

Question 10

What is a key attribute

Answer 10

an attribute of an entity in an entity type that has a unique value for each entity

eg Student_ID (of STUDENT)

CAN UNIQUELY IDENTIFY EACH ENTITY IN AN ENTITY TYPE

Key attribute underlined in ER diagram

Question 11

How are attributes displayed in the ER Diagram

Answer 11

As an oval connected to the entity

Question 12

How are multi valued attributes displayed in ER

Answer 12

as a double oval

Question 13

How are key attributes displayed

Answer 13

underlined

Question 14

How are composite attributes displayed

Answer 14

components connected to the oval representing the composite attribute

Question 15

What is an entity set

Answer 15

The current state of entities of that type that are stored in the database

Detailed desciption-
The set of of all the instances that are in the empty set along with the data of all those instances

eg :

Instance - car 1
123(registration) , blue (colour) …

Instance car 2
.
.
.

Question 16

What is the degree of a relationship type and hence what is a binary relation

Answer 16

The number of entity types the relationship affects

eg Works_ON - relates EMPLOYEE and PROJECT and so is a binary relation

Question 17

How are relationship types represent in an ER diagram

Answer 17

A diamond box where straight lines connect the relevant entity types

Question 18

What is a recursive relationship type

Answer 18

relation acts on one entity (unary relation)

eg employee supervises another employee
SUPERVISES is recursive

Question 19

Define and explain what a weak entity type is

Answer 19

An entity type that does not have a key attribute

.identified by the PARTICULAR ENTITY (that the weak entity is related to the particular entity)

AND

.a partial key ( that uniquely identifies weak entities that are related to the same owner entity

(participates in an identifying relationship type)

represented by a double rectangular box

eg:
DEPENDENT is a weak entity type
. A DEPENDENT entity is identified by the dependent’s first name,
and the specific EMPLOYEE with whom the dependent is related
. EMPLOYEE is its identifying entity type via the identifying
relationship type DEPENDENT_OF
. Name of DEPENDENT is the partial key

Question 20

what is total participation

Answer 20

Total participation in a relationship requires every entity in one set to participate.

In a university database, if “Enroll” has total participation ( where a student enrolls for a course )from “Student,” every student must be enrolled in at least one course.

Question 21

what is partial participation

Answer 21

If there is partial participation from the “Student” side in a relationship with “Course,” it means that not every student is required to be enrolled in a course. Some students may not be enrolled in any courses.

partial - some entities required to participate but others are not

Question 22

What is zero participation

Answer 22

Entities have the option of whether they want to participate in relationship

In a university database, if there is zero (optional) participation from the “Student” side in a relationship with “Course,” it means that some students may not be enrolled in any courses. They have the option to participate in the relationship, but it’s not mandatory.

Question 23

Instead of using cardinality ratio and existence dependency constrain we can use … instead

Answer 23

min , max notation

Question 24

How is total participation display in ER diagram

Answer 24

double line

Question 25

How is partial display

Answer 25

single line

Question 26

What is a derived attribute

Answer 26

An attribute whose value can be derived from one or more other related attributes

eg: Age can be derived from Date of Birth

represented as a dashed attribute in er diagram