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03 data modeling 1


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03 data modeling 1

  1. 1. Basics ofConceptual Data Modelling(Entity-Relationship Model)<br />
  2. 2. Element Types of the ERM<br />Entitytype represents an amountofsimilar (real-world) objects<br />Relationshiptype represents an amountofsimilarrelationsbetween(real-world) objects<br />Edge connectsentitytypeswithrelationshiptypes<br />Cardinality describeshowmanyrelations an entity must have (minimum) andcanhave (maximum) in theconnectedrelationshiptype<br />
  3. 3. Element Types of the ERM<br />Attribute representscharacteristicsof an entity type or relationship type<br />Key Attribute see Attribute; clearlyidentifiesinstancesofentitytypesrespectively relationship types ( also EntitysorRelationships)<br />Attribute Edge connects Attributes toEntity Type or Relationship Type<br />Generalization/Specialization splitsEntityTypesintoCategories mergesEntityTypes<br />Generalization/Specialization Edge connectsEntityTypeswithGeneralization / Specialization<br />
  4. 4. Example<br />Atuniversity, variousstudentsareenrolled:<br />
  5. 5. (0,n)-(0,n)-Relationship<br />Studentsstudycourses<br />
  6. 6. (1,1)-(x,n)-Relationship (x=0 v x=1)<br />Students live in Appartments(on theirownorwithotherstudents)<br />
  7. 7. (0,1)-(x,n)-Relationship (x=0 v x=1)<br />Every Appartmentcanhave a kitchen, <br />itis also possiblethat a KitchenbelongstomanyAppartments<br />
  8. 8. (0,1)-(x,n)-Relationship (x=0 v x=1)<br />A universityhasgotemployees. <br />Theyareorganizedhierarchically<br />(president -> professors -> phdstudents …)<br />
  9. 9. (0,1)-(01)-Relationship<br />A computeratuniversitycanhave an IP address(but need not becausethereare also stand alonecomputers).<br />Each IP addressthatbelongstotheuniversitycanbe<br />allocatedto a computer.<br />
  10. 10. (0,1)-(1,1)-Relationship<br />Eachpersoncanonlybut need not haveonedrivinglicence.<br />A drivinglicenceisdependent on a licence holder. <br />Drivinglicences do not „exist“ withoutthelicence holder<br />
  11. 11. Basics ofConceptual Data Modelling(Entity-Relationship Model)<br />