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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. 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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  1. Chapter 55 Data Modelling - Introduction Compiled by Eddie Moorcroft Source: P M Heathcote A level ICT

  2. 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:-

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. Diagram of DBMS System Purchasing programs Company Database Database Manage- ment System Sales programs Finance programs Payroll programs Personnel programs

  9. 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.

  10. 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.

  11. (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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