10. Fundamentals of Databases

Question 1

What is a Relational Database?

Answer 1

A Relational Database is a Database which stores information in Relations/Tables. Each Relation will consist of Records/Rows and Attributes/Columns.

Question 2

What is SQL?

Answer 2

SQL is Structured Query Language, a language for communicating with Relational Databases.

Question 3

What is a Primary Key?

Answer 3

A Primary Key is a unique identifier for each Record in a Relation.

Question 4

What is a Foreign Key?

Answer 4

A Foreign Key is an identifier for a Record in another Relation.

Question 5

What is a Composite Key?

Answer 5

A Composite Key is a Key (Primary or Foreign) which consists of multiple Attrributes.

Question 6

What is First Normal Form?

Answer 6

A Relation is in First Normal Form if it has no repeating Attribute or group of Attributes.

Question 7

What is Second Normal Form?

Answer 7

A Relation is in Second Normal Form if it is in First Normal Form and there are no Partial Key Dependencies.

A Partial Key Dependency is when an Attribute is dependent upon only part of a Composite Key.

Question 8

What is Third Normal Form?

Answer 8

A Relation is in Third Normal Form if it is in Second Normal Form and there are no Non-Key Dependencies.

A Non-Key Dependency is when an Attribute is dependent upon another Attribute which is not part of the Primary Key.

Question 9

Why do we Normalise Databases?

Answer 9

Normalisation removes repetition/redundancy in a Database which has the following benefits:

• Easier to update, as each value is only stored in one place. Repeating data can lead to an inconsistent Database.
• Quicker to search, as we have smaller Relations with fewer Attributes.
• Splitting data over multiple tables places constraints on how the the Database can be manipulated. These constraints may enforce Referential Integrity.

Question 10

Why do Databases implement Record Locks?

Answer 10

Record Locks prevent multiple users from changing the same Record in a Relation at the same time which can lead to inconsistent results or corrupt data.

Question 11

What is DeadLock?

Answer 11

DeadLock is when cyclical dependency appears between the Record Locks that users have created whilst interacting with a Database. For example user A may have locked Table 1 whilst waiting for user B to unlock Table 2, whilst user B is waiting for Table 1 to be unlocked to continue.