Helping find Database Candidate Keys, Primary Keys

Question

I am trying to work on this model and figure out the following questions about it:

1. What is (are) the candidate key(s) of PATIENT_VISIT?

2. If there is more than one candidate key, select a primary key from among the candidate keys.

3. Based on the primary key chosen, what normal form violations exist in PATIENT_VISIT?

4. Develop a solution that eliminates the normal form violations.
   Is your solution a lossless-join decomposition?

5. Is your solution dependency-preserving? If not, how can dependency preservation be achieved? Is this revised solution in BCNF?

6. Provide a solution that meets all three of the following conditions: (1) is in BCNF, (2) is dependency-preserving, and (3) is a lossless-join decomposition

    +---------+------------+------------+ | Patient | Hospital | Doctor | +---------+------------+------------+ | Smith | Methodist | D. Cooley | | Lee | St. Luke's | Z. Zhang | | Marks | Methodist | D. Cooley | | Marks | St. Luke's | W. Lowe | | Lou | Hermann R. | Duke | +---------+------------+------------+ 

In addition, suppose the following semantic rules exist.

• Each patient may be a patient in several hospitals.
• For each hospital, a patient may have only one doctor.
• Each hospital has several doctors.
• Each doctor uses only one hospital.
• Each doctor treats several patients in one hospital.

Answer 1

1. {Patient, Doctor} is a candidate key. The only other possible key is {Patient, Hospital, Doctor}, but that is not minimal because of the FD Doctor ⟶ Hospital; it is a superkey but not a candidate key.

2. Moot; there's only one candidate key.

3. The schema is not in BCNF because of the transitive dependency (FD) Doctor ⟶ Hospital. (Each attribute of the table is functionally determined by the key, the whole key, and nothing but the key.)

4. PD { Patient, Doctor }, DH { Doctor, Hospital }. This is a lossless decomposition.

5. This solution is dependency preserving.

6. See 4.