How does your ER diagram and schema change if a patient can undergo several surgeries (on di erent days, with possibly different surgeons) and if several surgeons can be involved in a single operation?
What will be an ideal response?
Solution:
Change to E-R diagram: dark arrow from patient to operation replaced by dark line.
Change to schema:
CREATE TABLE Operation (
Pid INTEGER,
Sid INTEGER,
Date DATE,
PRIMARY KEY (Sid, Date),
UNIQUE (Sid, Date),
FOREIGN KEY (Pid) REFERENCES Patient(Id),
FOREIGN KEY (Sid) REFERENCES Surgeon(Id))
Note: Adding constraint UNIQUE (Pid, Date) in an attempt to limit a patient to one
surgery a day will also eliminate the possibility of multiple surgeons performing a single
operation, so it is not included.
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