03 data modeling 1
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The document discusses the basics of conceptual data modeling using the entity-relationship model. It defines the main element types in an ERM including entity types, relationship types, edges, attributes, keys, and generalization/specialization relationships. It provides examples of how entities like students, courses, apartments, kitchens, employees, computers, people, and driving licenses can be modeled in an ERM using different relationship types and cardinalities.
03 data modeling 1
- 1. Basics ofConceptual Data Modelling(Entity-Relationship Model)
- 2. Element Types of the ERMEntitytype represents an amountofsimilar (real-world) objectsRelationshiptype represents an amountofsimilarrelationsbetween(real-world) objectsEdge connectsentitytypeswithrelationshiptypesCardinality describeshowmanyrelations an entity must have (minimum) andcanhave (maximum) in theconnectedrelationshiptype
- 3. Element Types of the ERMAttribute representscharacteristicsof an entity type or relationship typeKey Attribute see Attribute; clearlyidentifiesinstancesofentitytypesrespectively relationship types ( also EntitysorRelationships)Attribute Edge connects Attributes toEntity Type or Relationship TypeGeneralization/Specialization splitsEntityTypesintoCategories mergesEntityTypesGeneralization/Specialization Edge connectsEntityTypeswithGeneralization / Specialization
- 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)-RelationshipA computeratuniversitycanhave an IP address(but need not becausethereare also stand alonecomputers).Each IP addressthatbelongstotheuniversitycanbeallocatedto a computer.
- 10. (0,1)-(1,1)-RelationshipEachpersoncanonlybut need not haveonedrivinglicence.A drivinglicenceisdependent on a licence holder. Drivinglicences do not „exist“ withoutthelicence holder
- 11. Basics ofConceptual Data Modelling(Entity-Relationship Model)