Relational Databases

Question 1

What is the definition of a table?

Answer 1

A method for implementing an entity and attributes as a group of related data

Question 2

What is the definition of an entity?

Answer 2

An object about which data will be stored

Question 3

What is the definition of an attribute?

Answer 3

A characteristic or piece of information about an entity, which would be stored as a field in a relational database

Question 4

What is the definition of a primary key?

Answer 4

An attribute in each table that uniquely identifies each record

Question 5

What is the definition of a foreign key?

Answer 5

An attribute in a table that is a primary key in another table and is used to link tables together

Question 6

What is the definition of normalisation?

Answer 6

The process of ensuring that a relational database is structured efficiently

Question 7

What is the definition of a composite key?

Answer 7

Two or more attributes used in combination to key a primary key

Question 8

What is the definition of a relationship?

Answer 8

The link created between two entities

Question 9

How is first normal form achieved?

Answer 9

• Ensuring that a table does not contain repeating attributes or groups
• All the data in the table is atomic

Question 10

How is second norm form achieved?

Answer 10

• Ensuring database is in the 1NF
• Removing attributes that depend upon part of but not all of the primary key
-> by creating additional tables

Question 11

How is third normal form achieved?

Answer 11

• Ensuring the database is in 2NF

* Removing non-key attributes that depend upon other non-key attributes by creating additional tables

Question 12

What is the definition of a relation?

Answer 12

A relation is a data structure which consists of a heading and an unordered set of tuples which share the same type

Question 13

Name three key differences between flat file and relational databases.

Answer 13

• Flat file databases store all data in one table
• Flat file databases are less secure than relational databases
• Flat file databases are more likely to be subject to data redundancy
• Relational databases are more difficult to maintain

Question 14

What happens when relationships have been created between tables?

Answer 14

The tables become one database

Question 15

What technique must you use when deciding on how many tables are needed?

Answer 15

Normalisation

Question 16

What is the definition of an entity relationship diagram?

Answer 16

A visual method of describing relationships between entities

Question 17

What should any many-to-many relationships be replaced by?

Answer 17

One-to-many relationships

Question 18

What happens if not every record can be identified individually?

Answer 18

Relationships between tables cannot be made

Question 19

What are the three possible solutions for when records have the same primary key?

Answer 19

• Use a unique attribute
• Create a unique attribute
• Use a composite key

Question 20

When does redundant data occur?

Answer 20

Redundant data occurs when the same field is unnecessarily duplicated in two or more tables

Question 21

What is data inconsistency?

Answer 21

Data inconsistency is when the same data is stored multiple times

Question 22

What does it mean to store data at an atomic level?

Answer 22

Storing data at an atomic level means that the data cannot be further decomposed

Question 23

What are the three characteristics that a relational database design must have to be fully normalised?

Answer 23

• all data must be atomic
• should be no partial dependencies, where a non-key attribute depends upon part of but not all of the primary key
• should be no non-key dependencies, where a non-key attribute depends upon another bon-key attribute