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03 data modeling 1

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  • 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)