Databases

Entity

Entity

The item/person that the database is about

Primary Key

A unique identifier that is used to differentiate other entities

Secondary Key

A different, simpler + more common identifier to separate each entity

Foreign key

An attribute that links two tables together

Computerised database

Data that collects/stores data electronically

Flat file database

A single file that is suitable for storing one entity

Paper-based database

A method of collecting and storing data manually e.g. address book

Normalisation

Process of converting a database from 0NF to 3NF, it is used to organise data

Entity relationships

Helps the database to link two or more entities together

• One-to-one

• One-to-many

• Many-to-many

0NF (0 normal form)

First step of normalisation

1NF (first normal form)

• Must have a primary key in each table

• All fields must be unique

• Values in fields must be atomic

• No two records can be identical

2NF (second normal form)

• Data must be in 1NF

• Any partial dependencies must be removed (only one field should be dependant on the key)

3NF (third normal form)

• Data must be in 2NF

• Any transitive dependencies have been removed

  • “All fields are dependant on the key, the whole key and nothing but the key.”

Referential integrity

Process of ensuring consistency

• Prevents data from being deleted in a table if it is required somewhere else

Transaction processing

A single operation executed on data

Redundancy

Having one or more copies of the data in physically different locations to prevent damage/loss of the data

SQL (structured query language)

• Used to create and manage databases, it is useful for handling data + creating links between entities and tables

• Primarily a declarative language that expresses what needs to be achieved rather than expressing the logic of how it needs to be achieved

Relational Database

Linking two databases together using a foreign key