Relational Databases

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A database usually holds large collection of data organised especially for rapid search and retrieval.

A database is a logically coherent collection of data with some inherent meaning.


Data is raw facts and figures stored as independent units.


Information is data given context and meaning. It has been processed.


Data à Information =

·      Classifying

    -Categorise it

·      Selecting

                 -Find it

·      Sorting

    -Rearrange it

·      Summarising

    -E.g. Find Average

·      Calculating

    -E.g. work out VAT.

Databases can be used to share data with different computers and users.

It can also be used as reliable storage which can be accessed.

Efficiency and optimised.

Don’t need to care about physical formats.

They can also be used for communication.

File based system – redundancy and synchronisation issues.

File based systems are application focused.


Easy to create

Fast for specialised tasks



Data isolation

Data redundancy

Data dependence


Don’t support:

Centralised data definitions

Centralised access control

A database is a centralised store of data.

-       Single repository of data

Independent of individual applications

-       No one application dictates use


-       Contains a description of itself

Program/application independent

Designing the database:

Model data first – getting the requirements from users.

Design a single logical model of the data.

Identifies entities and relationships.

Database management software:

DBMS is the software which manages the database.

It sits between the application and the data.


-       Making changes to the structure of the data

-       Manipulating the data

-       Accessing the data

People who work with DBMS:

-       Database Admins

-       Designers

-       Application developers

-       End users

Types of DBMS:

-       Relational (main one for us!)

-       Network

-       Hierarchal

-       Object-orientated

-       Object relational

-       Associative


They improve:

-       Data redundancy

-       Data consistency

-       Data integrity

-       Adherence to standards

-       Control of security and access

-       Scalability


-       Complexity

-       Cost

-       Performance

-       Failure


 Idealised database development systems:

Databases are a part of information systems.

The database may be divided into levels/steps

-       Conceptual level (understand)

-       Logical level (design)

-       Physical level (implement)

We may need modelling techniques:

-       Entity-relationship models

-       Relational data models


Definition à Requirements à Design à Implementation à Testing à Maintenance

 Good data models:

-       Structural validity

-       Simplicity

-       Expressiblity

-       Non-redundancy

-       Share ability

-       Extensibility

-       Integrity

-       Diagrammatic representation

File à Stores data in a system

Database à Large store of related data

DBMS à Program for managing system

User à Person who accesses data in a database

Data model à Description of data

Essential concepts:

Data definition

Data manipulation

Data integrity

A relational system is a system in which:



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