Consider the following business rule: 'A professor may advise many students, but each student is assigned to only one advisor.' Which relationship type does this rule establish between the Professor and Student entities?"

Question

BlackTom AI · Accepted Answer

Cardinality describes how many instances of one entity relate to instances of another. Here, one Professor can advise many Students, while each Student is assigned to exactly one Professor. That is the definition of a one-to-many (1:M) relationship.

1. Relevant concepts
- Entity relationship cardinality (one-to-one, one-to-many, many-to-many, recursive).
- Direction matters: describe how many of entity B each instance of entity A may relate to, and vice versa.
- Implementation note: in a relational schema a one-to-many is usually implemented by placing the primary key of the “one” side as a foreign key in the “many” side (e.g., Student.professor_id -> Professor.id).

2. Step-by-step reasoning
- From Professor to Student: the business rule states “a professor may advise many students” → one professor can be linked to multiple student records.
- From Student to Professor: “each student is assigned to only one advisor” → each student record links to a single professor.
- Combine directions: one professor : many students, and each student : one professor → overall relationship is one-to-many (1:M).

3. No numeric calculations are required; the logical mapping above is sufficient.

4. Why the correct answer is correct
- One-to-many precisely captures the asymmetry: multiplicity on the professor side is one, on the student side is many. It also matches the standard implementation pattern (foreign key on Student pointing to Professor).

5. Why the other options are incorrect
- One-to-one (1:1): would require each professor advising at most one student and vice versa, which contradicts “may advise many students.”
- Many-to-many (M:N): would allow students to have multiple advisors, but the rule fixes students to only one advisor.
- Recursive relationship: describes an entity relating to itself (e.g., employee manages employee); here two different entities (Professor and Student) are involved.

Conclusion: The relationship type is One-to-Many (1:M), matching the provided answer (option d).

Consider the following business rule: 'A professor may advise many students, but each student is assigned to only one advisor.' Which relationship type does this rule establish between the Professor and Student entities?"单项选择题

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