1. Basics ofConceptual Data Modelling(Entity-Relationship Model)

2. Element Types of the ERM Entitytype represents an amountofsimilar (real-world) objects Relationshiptype represents an amountofsimilarrelationsbetween(real-world) objects Edge connectsentitytypeswithrelationshiptypes Cardinality describeshowmanyrelations an entity must have (minimum) andcanhave (maximum) in theconnectedrelationshiptype

3. Element Types of the ERM Attribute representscharacteristicsof an entity type or relationship type Key Attribute see Attribute; clearlyidentifiesinstancesofentitytypesrespectively relationship types ( also EntitysorRelationships) Attribute Edge connects Attributes toEntity Type or Relationship Type Generalization/Specialization splitsEntityTypesintoCategories mergesEntityTypes Generalization/Specialization Edge connectsEntityTypeswithGeneralization / Specialization

4. Example Atuniversity, variousstudentsareenrolled:

5. (0,n)-(0,n)-Relationship Studentsstudycourses

6. (1,1)-(x,n)-Relationship (x=0 v x=1) Students live in Appartments(on theirownorwithotherstudents)

7. (0,1)-(x,n)-Relationship (x=0 v x=1) Every Appartmentcanhave a kitchen, itis also possiblethat a KitchenbelongstomanyAppartments

8. (0,1)-(x,n)-Relationship (x=0 v x=1) A universityhasgotemployees. Theyareorganizedhierarchically (president -> professors -> phdstudents …)

9. (0,1)-(01)-Relationship A computeratuniversitycanhave an IP address(but need not becausethereare also stand alonecomputers). Each IP addressthatbelongstotheuniversitycanbe allocatedto a computer.

10. (0,1)-(1,1)-Relationship Eachpersoncanonlybut need not haveonedrivinglicence. A drivinglicenceisdependent on a licence holder. Drivinglicences do not „exist“ withoutthelicence holder

11. Basics ofConceptual Data Modelling(Entity-Relationship Model)