05  Transformation
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05 Transformation

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05 Transformation Presentation Transcript

  • 1. Transformation of ERMs into Relational Schemas
  • 2. Initial Situation
    Initial Situation: 3 Entity Types A, B und C
  • 3. Transformation Rules ERM  Tables
    Transformation Rules
    Describethetransformationfrom ERM modelsintorelations (tables)
    Are not alwaysunambiguous
    Simple Example: (x,n)-(x,n)-Relation (x=0 v x=1)
  • 4. (1,1)-(x,n)-Relation (x=0 v x=1)
  • 5. (0,1)-(x,n)-Relation (x=0 v x=1)
  • 6. (0,1)-(x,n)-Relation (x=0 v x=1)
  • 7. (0,1)-(0,1)-Relation
  • 8. (0,1)-(0,1)-Relation
  • 9. (1,1)-(1,1)-Relation
    Note: Itisnecessarytohave a triggerfornewentriesthatenforces an entry in thesecondrelation, as well.
  • 10. (1,1)-(1,1)-Relation
    Avoid (1,1)-(1,1) relations
    Better: Modelling as attributes
  • 11. (0,1)-(1,1)-Relation
  • 12. Remark: (1,x)-Relations (x={1,..,n})
    Example: (1,n)-(0,n)-Relations
  • 13. Remark: (1,x)-Relation (x={1,..,n})
    Example: (1,n)-(0,n)-Relation
  • 14. Remark: (1,x)-Relation (x={1,..,n})
    Example: (1,n)-(0,n)-Relation
  • 15. Generalization/Specialization
    How will Generalization/Specialization be modelled in Relations, meaning in Tables?
  • 16. Generalization/Specialization (N,P)
  • 17. Generalization/Specialization (N,T)
    Tosomeextend
  • 18. Generalization/Specialization (D,P)
    Tosomeextend
  • 19. Generalization/Specialization (D,T)
    Tosomeextend
  • 20. Triple Relationship Type
    Entries are arbitrary, as long as they are unique entries in A, B, and C.
  • 21. Reinterpreted Relationship Type (1/2)
    New entries not arbitrary. Theyaredependenton alreadyexistingentries in AB!
  • 22. Reinterpreted Relationship Type (2/2)
    Entries not arbitrary, because #C is Foreign Key
  • 23. Transformation of ERMs into Relational Schemas