Normalisation

Question 1

What is a relational database

Answer 1

When there is multiple tables in a database that relate to each other

Question 2

What is a table

Answer 2

A collection of records

Question 3

What is a record

Answer 3

A collection of fields

Question 4

What is a field

Answer 4

An column that stores a single data item

Question 5

What is a relation

Answer 5

A table

Question 6

What manages relational databases

Answer 6

The DataBase Management Systems (DBMS)

Question 7

What is a primary key

Answer 7

A field in a table that uniquely identifies each record in the table. No values in the primary key fields are repeated

Question 8

What is a super key

Answer 8

A combination of fields in a table which uniquely identifies each row.

Question 9

What are candidate keys

Answer 9

Minimal super keys. In other words there must be no attributes included in that do not contribute to the uniqueness of the rows. They are the possible options for the primary key

Question 10

What are the three types of keys

Answer 10

Super keys, candidaté keys, primary keys

Question 11

What is a composite key

Answer 11

A combination of two or more fields to form a primary key.

Question 12

Which is more serious deleting a record or an attribute ?

Answer 12

Deleting a record is removing an entire row of data whereas deleting an attribute is deleting an entire column. The seriousness depends on the data

Question 13

What is a database schema

Answer 13

When there is multiple tables in a database that relate to each other

Question 14

What does normalisation avoid

Answer 14

• Repeating groups
• Data redundancy
• Anomalies - update, insertion, and deletion
• complex queries

Question 15

What are repeating groups

Answer 15

A field that can have multiple values

Question 16

What is data redundancy

Answer 16

When the primary key is expanded

Question 17

What is an update anomaly

Answer 17

When the same data needs to be updated in more than one place

Question 18

What is an insertion anomaly

Answer 18

When records are added that do that satisfy the primary key requirements

Question 19

What is a deletion anomaly

Answer 19

When a deletion. Share unnecessary loss of data

Question 20

What is normalisation

Answer 20

The process of diving a set of data into smaller tables using a defined set of rules

Question 21

What are the characteristics of 1NF

Answer 21

No repeating groups
Choose a primary key

Question 22

What are the characteristics of 2NF

Answer 22

Relation is in 1NF
No partial dependencies

Question 23

What are the characteristics of 3NF

Answer 23

Relation is in 2NF
No transitive dependencies

Question 24

What is a dependency

Answer 24

When one field is related to another.

Question 25

What is a partial dependency

Answer 25

When a fields value is dependent on only part of a composite key

Question 26

What is a transitive dependency

Answer 26

When a fields value is dependent on a non-primary key field

Question 27

What is derived data

Answer 27

When you use a field to calculate another. Derived data is not stored

Question 28

What is duplicate data

Answer 28

When a record has the same value for a field of another record.

Question 29

What is the difference between duplicate data and data redundancy

Answer 29

Data redundancy is produced by repeating groups in the first normal form hence it must be removed to normalise the table whereas duplicate data is not wrong must not be removed. Eg two students living in the same road

Question 30

What is atomic data

Answer 30

When each value of a field stores a single data item.

Question 31

What is the difference between dependency and derived data

Answer 31

Dependency does not involve calculation but rather is a relationship between two fields whereas derived data is calculated from another field and is not stored.

Question 32

What is a foreign key

Answer 32

A field in a table that is a primary key in another table

Question 33

What is referential integrity do

Answer 33

It prevent the insertion of a data that refers to other data that doesn’t exist and the removal of data that relates to other data

Question 34

What does a one to one relationship entail

Answer 34

Both fields are put in the same table