1.7 Databases

Database

An organised collection of data which can be accessed in many different ways.

Flat Files

Database where all the data is stored in a single table. Column headings are field name.

Problems of Flat Files

• Data Duplication

• Inconsistencies can arise

• Restrictive

Flat Files Data duplication

Data is entered more than necessary

Flat files inconsistencies

A change of data could result in some records having the updated data whilst others having the old one.

Flat Files Restrictive

Only suitable for small and simple stores of data

Relational Files

A large collection of data items stored in two or more tables, containing links so links so data can be accessed more ways.

Disadvantages of Relational

• More complex

• Expensive

Data Consistency

Certain data can be found in many tables simultaneously. If one data is changed, all locations of that data must also be changed. If there is no central pool of data, the database may soon be inconsistent.

Data Redundancy

Process of reducing redundant data, not completely eliminating duplication.

Data Integrity

Refers to the correctness of the data. Once an inaccurate data is discovered, the user starts to lose faith in all the data.

Data Independence

The changing of data without changing the application which processes that data.

Primary Key

A piece of information unique to that record in a database

Foreign Key

Any field which is a primary key in another table

Views of Database Systems

The process of restricting access to certain users

Advantages of Views of Databases

Allows only that part of the database to be read/edited/deleted
Users can only edit parts of the records
May link tables to form a table in the user’s view

Disadvantages of Views of Databases

Users with limited access may struggle to analyse data

First Normal Form

All recorded data are referenced by a key

Second Normal Form

Attributes depend on the entire key

Third Normal Form

Depend on nothing, but the key