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04 data modeling 2

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  • 1. AdvancedConceptual Data Modelling(Entity-Relationship Model)
  • 2. Reinterpreted Relationship Types
    When to use a Reinterpreted Relationship Type?
    Simple Case: If a relationship type is not used for connections to other model elements, he stays uninterpreted.
    If a relationship type is used for further modelling, he will either be reinterpreted or will become a multiple relationship type (n>2).
  • 3. Generalization/Specialization (N,P)
    Therearevariousformsofstudents.
    The relationship is non-disjunct (N) because a PhDstudent in thesubject
    informationsystemscan also be a bachelorstudent in philosophy.
    The relationship is partial (P) becausethereare also othertypesof
    Students such asmasterstudents, executivemasterstudents, etc.
  • 4. Generalization/Specialization (N,T)
    An animalcanbe male orfemaleorboth (e.g. snail) (not disjunct (N)).
    Therearenootherformsofsexuality (T).
    Tosomeextend
  • 5. Generalization/Specialization (D,P)
    A personcaneitherbe a man or a woman (D).
    Thereare also othertypesliketransexuals (P)
    whoareneitherwomannor man.
    Tosomeextend
  • 6. Generalisization/Specialization (D,T)
    A personcaneitherbe a male or a femaleperson (D).
    Therearenoothertypes (T).
    Tosomeextend
  • 7. Modelling Conventions (Summary)
    Key Attribute consistof
    Name oftheEntity Type
    „ID“ or „Nr“
    andhavetobeunderlined
    Non-Key Attributes will not beunderlined
    Key Attributes will bemodelledtoEntityTypesexclusively.
    Howandwhatkeys a relationship type receivesis due toitscardinalities. They will notbemodelled.
    The same is valid forForeignKeys.
    Additional Non-Key Attributes of a Relationship Type will bemodelled. Itisonlypossiblewith(x,n)-(x,n) relations (x=0 v x=1).
  • 8. AdvancedConceptual Data Modelling(Entity-Relationship Model)