1. Conceptual Design Revision Database Development

2. Basic constructs of the Entity Relationship Model Entity  Representation of an Entity on an ER diagram is: –a box with square corners –labelled with the entity name. Note – the entity name is always singular Student

3. Basic constructs of the Entity Relationship Model Weak Entity  Representation of a Weak Entity on an ER diagram is: –a box with rounded corners –labelled with the entity name (singular) NextOfKin

4. Basic constructs of the Entity Relationship Model Strong Entity  By default an entity which is not a weak entity is a strong entity. Student

5. ER Model Relationship Types One to One –An employee is allocated a single parking space, a parking space belongs to only one employee. 1:1 Employee ParkingSpace

6. ER Model Relationship Types One to Many –A department has many employees assigned to it, each employee is assigned to only one department. 1:M Department Employee

7. ER Model Relationship Types Many to Many –An employee attends many staff development sessions, each staff development session is attended by many employees. N:M StaffDevSess Employee

8. ER Model Relationship Types Many to Many –An employee attends many staff development sessions, each staff development session is attended by many employees. N:M StaffDevSess Employee

9. ER Model Relationship Types Inheritance –A technician is a kind of employee about whom we wish to record, in addition to his other attributes, his highest technical qualification. Technician Employee

10. ER Model Relationship Existence  In the ER model optional association existence is shown as.  An employee may be a member of one of the works football teams. 1:M FootballTeam Employee

11. ER Model Relationship Existence  In the ER model mandatory association existence is shown as.  An employee must be a member of one of the unions recognised by the company. 1:M Union Employee

12. ER Model Relationship Recursive relationship.  An employee may also be a manager. A number of employees are managed by a single manager Employee 1:M Employee Manager

13. Attributes What is an attribute?  An attribute is a piece of information about the object or event that we wish to store in our database.  It can be said to describe the object.  An example of some possible attributes for Employee could be EmployeeID, EmpFirstName, EmpSurname

14. ER Model Representation of Attributes  Only attributes which uniquely identify an entity will be represented on your ER diagram.  A key attribute may be represented as follows Employee EmployeeID

15. ER Diagram STUDENT HALL N:1 StudentID HallName Entity Entity Name Relationship Cardinality Attribute Attribute name Mandatory Existence Optional Existence

16. Diagram Script Entity nameAttributes IdentifiedSynonymRelated to Coursetitle courseCode PrerequisiteStudent Class Course StudentstudentID studentName address postcode Course Classsemester classRoom uniqueClassName tutor Course Relationship between course and student gradeCourse and Student

17. Using the Information Base  Where do we start?  Analyse the information gathered during the requirements analysis. –One element at a time

18. Identifying Entities  A noun is a word that names a person or thing  A noun phrase is a group of words that operate like a noun e.g. dentist appointment  Consider each noun or noun phrase and determine if it is a candidate entity.  Reasons for rejecting candidate entities.

19. Rejecting Candidate Entities  Redundancy  Vagueness  An event or operation  Meta Language  Outside the system boundary  Attribute

20. Next Week  In-class test