1. Data Modelling

2. ICT5 Introduction Historical development with most organisations Small-scale origins Individual computers bought for particular applications Typically batch-processed billing systems and payroll Gradual development of systems for other departments Systems developed independently Many files created, often with different data structures to suit different programs and even different operating systems

3. ICT5 Problems with traditional approach Data redundancy data duplicated in many different files. Data inconsistency same data held in different files has to be updated in each separate file when it changes. Program-data dependence Every computer program has to specify exactly what data fields constitute a record in the file being processed. Changes in data structure result in changes to programs Lack of flexibility Difficult and time-consuming to assemble the data from the various files and write new programs to produce the required non-routine reports. Data was not shareable If one department had data that was required by another department, it was awkward to obtain it.

4. ICT5 The Database approach The concept of a database was born out of a need to solve the problems caused by the flat-file systems Database A collection of non-redundant data shareable between different applications Company data to be centralised in a common resource for access by any application Although solving problems of redundancy and inconsistency, new problems were created: Unproductive maintenance – programs were still dependent on data structure, so changes required by one department would require all programs using that data structure to be changed. Lack of security – all data could potentially be accessed by all applications

5. ICT5 Database Management System A DBMS is a layer of software inserted between the data files and the applications This software goes some way to solving the remaining problems Two essential features are: Program-data independence User / application does not need to be aware of the data storage structure User access restrictions Each user is limited to applicable data

6. ICT5 The conceptual data model From the statement of data requirements a conceptual data model is produced. This describes how the data elements in the database are to be grouped. Three terms are used to describe the data requirements: An entity is a thing of interest to an organisation about which data is to be held Examples of entities include Customer, Employee, Stock Item, Supplier. An attribute is a property or characteristic of an entity Examples of attributes associated with a Customer include Customer ID, Surname, Initials, Title, Address, Credit Limit. A relationship is a link or association between entities An example is the link between Dentist and Patient; one dentist has many patients, but each patient only has one dentist.

7. ICT5 Types of relationship There are only three different ‘degrees’ of relationship between two attributes. A relationship may be: One-to-one e.g. the relationship between Husband and Wife, or between Householder and Main Residence One-to-many e.g. the relationship between Mother and Children, between Customer and Order, between Borrower and Library Book Many-to-many e.g. the relationship between Student and Course, between Stock Item and Supplier, between Film and Film Star

8. ICT5 Entity-relationship diagrams An entity-relationship diagram is a diagrammatic way of representing the relationships between the entities in a database. EmployeeCompany car drives (One-to-one) WardPatient holds (One-to-many) AlbumSingers features (Many-to-many)

9. ICT5 A hospital in-patient system A hospital is organised into a number of wards. Each ward has a ward number and a name recorded, along with a number of beds in that ward. Each ward is staffed by nurses. Nurses have their staff number and name recorded, and are assigned to a single ward. Each patient in the hospital has a patient identification number, and their name, address and date of birth are recorded. Each patient is under the care of a single consultant and is assigned to a single ward. Each consultant is responsible for a number of patients. Consultants have their staff number, name and specialism recorded.

10. ICT5 Exercise on In-patient system 1. State 4 entities for the system giving a suitable identifier for each entity. 2. Draw an entity-relationship diagram to show the relationships between the entities.