Which of the following Functional Dependencies could involve a partial dependency?

Question

BlackTom AI · Accepted Answer

Question restatement: Which of the following Functional Dependencies could involve a partial dependency?

Option A: AppointmentID --> PatientName, PatientPhone
- Analysis: If the relation has a composite primary key (for example, (AppointmentID, PatientID) or (AppointmentID, something else)), then a dependency where AppointmentID (a part of a composite key) determines some non-prime attributes could represent a partial dependency. However, AppointmentID alone is often a candidate key by itself in many appointment schemas, meaning it would be a full dependency rather than partial if AppointmentID is a candidate key. The partial-dependency interpretation hinges on whether AppointmentID is merely a part of the candidate key rather than the whole key. Without knowing the exact key definition, this option could be a partial dependency only if AppointmentID is a subset of a composite candidate key, not a full key itself.

Option B: AppointmentDate --> PatientID, PatientName, PatientPhone, AppointmentLocation
- Analysis: This says a date determines many attributes across potentially different patients and appointments. If the candidate key were composite and included AppointmentDate as a component, AppointmentDate would be a part of the key. But typical designs do not use AppointmentDate as a component of a candidate key; it more often serves as a non-key attribute. Consequently, this is unlikely to represent a partial dependency, and it more likely describes a non-key to attribute dependency or an unusual schema where Date is part of a composite key. It does not clearly illustrate a partial dependency in the common sense.

Option C: PatientID --> PatientName, PatientPhone, AppointmentLocation
- Analysis: Here, PatientID (which identifies a patient) determines the patient’s name and phone, which are reasonable functional dependencies. Importantly, AppointmentLocation being determined by PatientID suggests that the location is tied to the patient rather than to a specific appointment. If the relation’s candidate key is a composite such as (PatientID, AppointmentID), then PatientID is a part of that key. In that case, these dependencies could be partial dependencies because a subset of the key (PatientID) determines some non-prime attributes. The inclusion of AppointmentLocation under PatientID reinforces that some attributes depend on part of the composite key rather than the whole key.

Option D: PatientID, AppointmentID --> PatientName, PatientPhone, AppointmentDate, AppointmentLocation
- Analysis: This left side is the full composite key (both PatientID and AppointmentID together). Dependencies where the whole key determines attributes are full dependencies, not partial. Since the left side constitutes the entire candidate key, this option does not illustrate a partial dependency.

Summary of reasoning: To identify a partial dependency, we look for a dependency X --> Y where X is a proper subset of a candidate key (i.e., part of a composite key) and Y is a non-prime attribute. Option C most clearly fits the classic partial-dependency scenario if the table’s candidate key is the composite (PatientID, AppointmentID), since PatientID is a subset of that key and determines several non-prime attributes. Option A could be a partial dependency only under a schema where AppointmentID is part of a composite key rather than a standalone key, which is less common. Option B does not clearly present a partial dependency given typical key structures. Option D uses the full key, which by definition is not partial.

Which of the following Functional Dependencies could involve a partial dependency?单项选择题

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