1. Conceptual Modelling The Entity-Relationship (ER) Model The ER diagram Data Modelling

2. Conceptual Data Models A conceptual model of the data on which the IT systems of an organisation are based Independent of implementation Stable over time Conceptual data structure doesn't change as much as functionality Conceptual models are to be transformed to a database model as the relational model

3. ER Model: Concepts Entities Attributes Atomic Composite Multi valued Attribute values Entity types Keys Domains Relations Cardinality ratio Participation (total / partial) Relations may have attributes Weak Entity Types Identifying owner Identifying relation Partial key A weak entity always has total participation in the identifying relation.

4. An Example: The Company Database s.61 i bogen

5. Entity Types in the Company Database Department: name, number, location Project: name, number, location Employee: ssn, bdate, name (poss. composite), sex, address (poss. composite), salary Dependent (weak?): name, sex, bdate

6. Relations in the Company Database Manages Works_For Works_On Dependents_Of Supervision Controls

7. ER Diagram for the Company Database

8. Relations of Degree > 2

9. Often causes problem in database design May be transformed to binary relations or entities

10. Relations of Degree > 2 Is this correct?

11. Relations of Degree > 2 Is this better?