Entity-Relationship (ER) Diagrams
===================================
Close up on participation constraints:
--------------------------------------
Ternary relationship:
AdvisedBy(StudentRIN, MajorCode, FacultyRIN)
Key: StudentRIN, MajorCode
Students Major -> Faculty
Binary Model:
R1(StudentRIN, MajorCode)
R2(StudentRIN, FacultyRIN)
R3(FacultyRIN, MajorCode)
Decomposition!
S F M
s f1 m
s f m2
s3 f m
Cannot apply s m -> f
Lossy decomposition: representing ternary relationship in three binary
relationship does not give me the same exact result!
----------------
Alternate model:
Ternary relationship:
AdvisedBy(StudentRIN, MajorCode, FacultyRIN)
Keys: StudentRIN MajorCode, StudentRIN FacultyRIN
Students Major -> Faculty
Faculty -> Major
Binary Model:
R1(StudentRIN, MajorCode)
R2(StudentRIN, FacultyRIN)
R3(FacultyRIN, MajorCode)
Decomposition!
S F M
s f1 m
s f m2
s3 f m
f -> m
S F M
s f m <-- lossless decomposition
s f m2
s3 f m