04 data modeling 2

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04 data modeling 2

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

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