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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

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
ad