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 Company Database Manage- ment System Sales programs Purchasing 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. 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. Joe Bloggs, 25/03/83, 012345

11. Entity-relationship diagrams EmployeeCompany car drives (One to One) WardPatients holds (One to Many) CD AlbumSingers features (Many to Many)