Describe the relationship between TEACHER and DEPARTMENT

Question

BlackTom AI · Accepted Answer

The TEACHER table contains a non-nullable foreign key deptnumber pointing to DEPARTMENT, so each teacher record is assigned exactly one department.

1) Relevant concepts: relational schemas use foreign keys to express relationships; cardinality (one, many) and optionality (mandatory vs optional) are read from relationship notation. A single straight bar (|) next to an entity indicates “one and only one”; a crow’s foot indicates “many”; a circle indicates “zero (optional)”.

2) Step-by-step reasoning:
- Inspect the TEACHER entity: it has an attribute deptnumber (not a primary key). That attribute is the FK that references DEPARTMENT.deptnumber.
- The relationship connector shows a single straight line (mandatory one) at the TEACHER end and a crow’s-foot at the DEPARTMENT end. That notation means: from the TEACHER perspective the multiplicity is exactly 1; from the DEPARTMENT perspective multiplicity is many.
- A non-nullable FK plus the mandatory-one notation means a teacher cannot exist without being assigned to a department.

3) Intermediate deduction steps:
- Presence of deptnumber in TEACHER ⇒ TEACHER belongs to some DEPARTMENT.
- Mandatory indicator (no circle) ⇒ deptnumber cannot be null ⇒ that “some” must always exist.
- Crow’s-foot at DEPARTMENT ⇒ a department may relate to many teachers.

4) Why the correct answer is correct:
Because every TEACHER record has a single, required deptnumber FK, the mapping from TEACHER to DEPARTMENT is one-to-one in the sense “one TEACHER → one DEPARTMENT” (and that one is required). Simultaneously the inverse is one-to-many (one department → many teachers), but the question asks the relationship from TEACHER’s perspective, so it is “1 and only 1 Department.”

5) Why other options are incorrect:
- “0 to 1” would allow a teacher to have no department; the FK is mandatory so this is false.
- “1 to Many / 0 to Many / Many” that imply a teacher can link to multiple departments — not possible because TEACHER stores only a single deptnumber.
- Options phrased about “Many Teachers are associated 1 Department” describe the inverse direction (true as a statement about DEPARTMENT), but they do not match the teacher-centric wording required by the question.
- “No relationship” is false because the FK and connecting line explicitly show a relationship.

Conclusion: The correct characterization is “1 Teacher is associated with 1 and only 1 Department,” which matches the provided answer.

Describe the relationship between TEACHER and DEPARTMENT单项选择题

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