Difficulty: Easy
Correct Answer: Correct — that is the definition of a composite key
Explanation:
Introduction / Context:
Schema designers often need multiple attributes to uniquely identify a tuple. When more than one attribute participates jointly in uniqueness, the resulting key has a specific name and properties.
Given Data / Assumptions:
Concept / Approach:
A composite (or compound) key is exactly a key composed of two or more attributes. It can be a candidate key or the chosen primary key. The definition does not depend on normal form, foreign keys, or whether the attributes are natural or surrogate.
Step-by-Step Solution:
Verification / Alternative check:
Example: Enrollment(student_id, course_id, term) might have primary key (student_id, course_id, term). This three-attribute primary key is composite.
Why Other Options Are Wrong:
Common Pitfalls:
Confusing composite keys with concatenated values; assuming composite keys cannot be primary keys (they can); believing composite implies cross-table linkage (it does not).
Final Answer:
Correct — that is the definition of a composite key
Discussion & Comments