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 integrity is the maintenance of, and the assurance of the accuracy and consistency of, data over its entire life-cycle, and is a critical aspect to the design, implementation and usage of any system which stores, processes, or retrieves data. 

 

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.

Advantages:

Easy to create

Fast for specialised tasks

Cheap

Problems:

Data isolation

Data redundancy

Data dependence

Limited

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

Self-describing

-       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.

Controls:

-       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

Advantages:

They improve:

-       Data redundancy

-       Data consistency

-       Data integrity

-       Adherence to standards

-       Control of security and access

-       Scalability

Disadvantages:

-       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

Analogy

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

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