Untitled

Página 1

Databases

A collection of non-redundant data shareable between different application (software).

There

are two types of databases:

Flat file

Relational

Flat-file:

This is a single table database with

separate copies of data in each part of the business.

An example could be a phonebook.

Problems with flat-file:

Data

duplication

Wastes disk space and slows down query

time.

Maintenance

Every instance of a piece of data needs

to be updated if changed.

Error

More reliance on manual data entry means

that data is more likely to contain errors.

Relational databases:

A collection of related files organised.

Data is divided into logical groups and

stored in multiple tables. The tables are then connected to each other through

relation.

Characteristics:

Data is stored in a set of tables

Tables are joined using relational links

Reduces duplication of data in database

Data is normalised

Allows for greater flexibility and

efficiency

Relationships:

Each table must have a unique reference

for each record – primary key

A composite

primary key is where the p.k

consists of several data items

Linking a p.k to other tables creates the foreign key

Foreign key are the relationships which

links the tables together

New Page