Database ( 2 )

Question 1

what is a relational database?

Answer 1

A collection of tables in which relationships are modelled by shared attributes

Question 2

How is data held in a relational database?

Answer 2

Data is held in relations ( tables ), and the relations are linked through common attributes

Question 3

What each column in a relation represent?

Answer 3

One Attribute

Question 4

What does each row in a relation represent?

Answer 4

One record

Question 5

How is the entity represented in a relational table algebra?

Answer 5

Entity name is shown outside brackets, everything else is within brackets

Question 6

How are attributes represented in relational table algebra?

Answer 6

Attributes are listed inside the brackets

Question 7

How is the primary key represented in relational table algebra?

Answer 7

Underlined

Question 8

Why is an index created?

Answer 8

• An index of primary keys is automatically created by the database software, giving the position of each record according to its primary key
• Needed to allow a particular record to be located very quickly.

Question 9

Why are secondary keys created & indexed?

Answer 9

To allow even quicker searches, where only a primary key exists, searches would have to be done individually, which would be slower

Question 10

What is normalisation?

Answer 10

A processed used to come with the best possible design for a relational database

Question 11

What are the requirements of a database design?

Answer 11

• No data is unnecessarily duplicated
• Data is consistent throughout the database ( consistency comes with not holding any duplicated data ), this is to prevent anomalies when data is inserted/deleted
• Structure of each table is flexible enough to allow you to enter as many or as few times as required
• Structure should enable a user to make all manners of queries relating data from different tables