Chapter 16 Database Concepts

Question 1

What is a database?

Answer 1

structured and persistent store of data that is used on a computer system

Question 2

What is an entity?

Answer 2

Object that data can be stored about

Question 3

Example of an entity?

Answer 3

customers, products,sales

Question 4

What does an entity become in a database?

Answer 4

A table

Question 5

What is an attribute? What will it become in a table?

Answer 5

Something that an entity has , a property of it e.g. an entity of Products may have product id, stock, price etc.

It will become the columns

Question 6

What do databases allow us to do?

Answer 6

• retrieve data quickly
• be updated easily
• change the view of it (for us or limit users)
• in 3NF avoids redundancy and limits storage use

Question 7

meaning of structured in the definition of a database?

Answer 7

data i organised for ease of processing

Question 8

meaning of persistent in the definition of a database?

Answer 8

can’t be lost, stored on secondary storage

Question 9

What is a record?

Answer 9

a row in a table, it contains a number of fields containing data relating to a specific item within an entity

Question 10

What is a field?

Answer 10

Something that stores one piece of data. property of an record in an entity

Question 11

What does atomic mean?

Answer 11

Cannot be broken down anymore

Question 12

What is a flat file database?

Answer 12

A database that consists of a single file/ entity

Question 13

What would a flat file database be suitable for ?

Answer 13

e.g. all members in a club

Question 14

What do flat file databases cause?

Answer 14

a lot of redundancy

Question 15

What is redundancy?

Answer 15

• unnecessary repetition of data

- leads to inconsistencies

Question 16

How is an entity usually written?

Answer 16

Entity1(Attribute1,Attribute2,Attribute3)

e.g. Customers(CustomerID,DOB,Address,Phone Number)

Question 17

What is special about flat file databases?

Answer 17

They’re unnormalised

Question 18

What is another name for a fields/row?

Answer 18

A tuple or a record

Question 19

What is a primary key? - only relational databases

Answer 19

a unique identifier of each record in an entity

Question 20

What is a secondary key? - relational databases

Answer 20

secondary key is a unique attribute used for indexing

Question 21

When would a secondary key be useful? - example

Answer 21

When a customer calls with an enquiry about an order they may not know their ID so a secondary identifier can be used e.g. surname

Question 22

What does secondary key allow?

Answer 22

quicker searching and easier identification(as possibilities become smaller)

Question 23

What is a relational database?

Answer 23

Database where there is more than one entity, which share attributes using foreign keys

Question 24

What is a foreign key?

Answer 24

A primary key used as an attirbute of another table used to link the entities together. Essentially a primary of the entity that one entity is linked with.

Question 25

What is a foreign key used for ?

Answer 25

Linking entities in a relational database

Question 26

What does having a relational database reduce? How?

- what does this improve

Answer 26

Data redundancy. As foreign keys are used to put primary keys into other tables - those are entered once

increases accuracy and consistency of data

Question 27

What are the three types of relationships between entities

exmple for each

Answer 27

one to one - husband to wife
one to many - mother and child
many to many - student and course

Question 28

What is a one to one relationship?

Answer 28

where one entity can be linked to only one entity

e. g. tutor and office
e. g. headteacher and school

Question 29

What is a many to many relationship?

Answer 29

where multiple entites can be linked to multiple entities

e. g. teacher and student
e. g. student and course

Question 30

What is a one to many relationship?

Answer 30

where one enity can be linked to many entites

e. g.customer and order
e. g. borrower and library books

Question 31

How can we show relationships between entites visually?

Answer 31

using entity relationship diagrams

Question 32

What is a composite key?

Answer 32

where 2 or more attributes are used to describe a primary key

Question 33

What is indexing

Answer 33

The process of creating a database structure called index which will improve speed of retrieval of data

Question 34

Using entity relationship diagrams how will a one to one relationship be shown?

Answer 34

By a line

Question 35

Using entity relationship diagrams how will a one to many relationship be shown?

Answer 35

By a line with a chicken foot by the entity of many

Question 36

Using entity relationship diagrams how will a many to many relationship be shown?

Answer 36

Firstly a new entity will be created. Which will be in the middle and be connected by a chicken foot both sides. Then there will be a one to many relationship between the new enitity and original entities with the new entity being the many!

Question 37

Do flat file databases have a foreign key?

Answer 37

NO

Question 38

When we have new entity created to show many to many relationship what is the name of the key of the new entity?

Answer 38

A composite key

Question 39

What is used with indexing ?

Answer 39

a secondary key

Question 40

What are the 4 types of query?

Answer 40

select (can be used for filter and sort),append,update,delete

Question 41

What is a report?

Answer 41

A query of data from a database which is presented in a readable and clear way.

Question 42

What is a query?

Answer 42

an action on a database

Question 43

Another name for a table in a relational database?

Answer 43

relation