ERD:

Scenario:

The above ERD represents the details of a simple course database which records the course registration details of students. The course entity has a unique identifier CourseNum and the Registration entity is allocated a partial key. The mode represents the mode of registration: online or on-campus. A student may have more than one phone number.

Semantic Rules:

1. Each course may have many registrations.
2. Many registrations are recorded for each course.
2. Each student may register only once.
2. Each student can have multiple registrations.

Question: Which of the following functional dependencies represent full functional dependency?

Question

ERD:

Scenario:

The above ERD represents the details of a simple course database which records the course registration details of students. The course entity has a unique identifier CourseNum and the Registration entity is allocated a partial key. The mode represents the mode of registration: online or on-campus. A student may have more than one phone number.

Semantic Rules:

1. Each course may have many registrations.
2. Many registrations are recorded for each course.
2. Each student may register only once.
2. Each student can have multiple registrations.

Question: Which of the following functional dependencies represent full functional dependency?

BlackTom AI · Accepted Answer

We start by identifying the concept at play: full functional dependency means that a non-key attribute is functionally determined by the whole candidate key, and not by just part of a composite key. Now, let's examine each option in turn.

Option 1 (A): 'CourseNum --> Name, Description' and 'RegistrationNum,CourseNum --> RegistrationDate, Mode'.
- For the Course relation, CourseNum is the key and determines Name and Description. Since CourseNum is a whole key for that relation, this FD is a full functional dependency in the Course relation.
- For the Registration relation, the combined key (RegistrationNum, CourseNum) determines RegistrationDate and Mode. Because the determinant is the entire composite key, this is also a full functional dependency within the Registration relation.
So, both FDs in this option represent full functional dependencies.

Option 2 (B): 'StudentNum --> Name, Phone, Email'.
- If StudentNum is the key for the Student relation, then it functionally determines Name, Phone, and Email. This is a full functional dependency as well, since the determinant is the (single-attribute) key of that relation.
Thus, this is also a correct example of a full functional dependency.

Option 3 (C): 'RegistrationNum,CourseNum --> RegistrationDate, Mode'.
- This repeats the same full FD seen in option A for the Registration relation: the entire composite key (RegistrationNum, CourseNum) determines RegistrationDate and Mode. This is a classic full functional dependency.

Option 4 (D): 'RegistrationNum,CourseNum --> RegistrationDate, Mode' and 'StudentNum --> Name, Phone, Email'.
- This option combines the two FDs from options 2 and 3 (and 1) that are each full functional dependencies in their respective relations. Since both parts describe full dependencies on their respective keys, the whole option represents multiple full FD statements.

In summary, all listed FDs describe full functional dependencies: the determinant is either the whole candidate key of the relation or a single-attribute key where appropriate. Each statement correctly reflects a full FD, and Option D simply groups the already-valid full FDs from the other options into one combined choice.

类似问题

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