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