Chapter 55 data modelling introduction
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Chapter 55 Data Modelling - Introduction. Compiled by Eddie Moorcroft Source: P M Heathcote A level ICT. Traditional file approach. Most organisations began information processing on a small scale, by computerising each department independently, one by one.

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Chapter 55 Data Modelling - Introduction

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Chapter 55 data modelling introduction

Chapter 55 Data Modelling - Introduction

Compiled by Eddie Moorcroft

Source: P M Heathcote A level ICT


Traditional file approach

Traditional file approach

  • Most organisations began information processing on a small scale, by computerising each department independently, one by one.

  • Files of information relevant to one department were created and processed by dozens of separate programs.

  • This led to many problems:-


Problems with traditional approach

Problems with traditional approach:

  • Data redundancy

    • The same data duplicated in many different files.

  • Data inconsistency

    • Data that is duplicated, and not updated when changed in all files

  • Program-data dependence

    • The computer program requires the data to be in a particular format, changing the format requires every program using that file to be changed.


Problems with traditional approach continued

Problems with traditional approach - continued

  • Lack of flexibility

    • In such a system, when information of a non-routine nature is needed, it may take weeks to assemble the data from various files.

  • Data not shareable

    • If one department has data that was required by another, it can be awkward to obtain it.


The database approach

The database approach

  • A database is defined as:“a collection on non-redundant data shareable between different applications”

  • Thus, all data belonging to the entire organisation would be centralised in a common pool of data, accessible by all applications.


Problems with the database approach

Problems with the Database approach

  • Unproductive maintenance

    • Programs still depend on the structure of data files, so if one department required to add an extra field, all programs would need to be altered.

  • Lack of security

    • All the data in the database, even confidential or sensitive data, is accessible by all applications.


The database management system dbms

The Database Management System (DBMS)

  • This is a layer of software inserted between the applications and the data, which attempts to solve the problems of “Unproductive maintenance” and “Lack of Security”

  • Two features of DBMS are:

    • Program-data independence

    • Restricted user access


Diagram of dbms system

Diagram of DBMS System

Purchasing

programs

Company

Database

Database

Manage-

ment

System

Sales

programs

Finance

programs

Payroll

programs

Personnel

programs


Conceptual data model

Conceptual data model

  • A database is designed based on the information it will hold. The requirements are defined in terms of:

  • An entity

    • a thing of interest to an organisation, about which the data is to be held – e.g. customer, employee, stock item, etc.


Conceptual data model continued

Joe Bloggs,25/03/83,012345

Conceptual data model - continued

  • An attribute

    • a property or characteristic of an entity – e.g. attribute associated with a student are, surname, forename, date of birth, admission number etc.

  • A relationship

    • the links or association between two entities, e.g. between school and pupil, a school contains many pupils, but a pupil only goes to one school.


Entity relationship diagrams

(One to One)

Employee

Company car

drives

(One to Many)

Ward

Patients

holds

(Many to Many)

features

CD Album

Singers

Entity-relationship diagrams


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