Key terminology — decide whether the following claim is correct: “Keys made up of two or more attributes are called composite keys.” Provide the best evaluation.
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ACorrect — that is the definition of a composite key
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BIncorrect — composite keys require foreign keys
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CIncorrect — composite keys must be surrogate keys
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DOnly sometimes correct — depends on BCNF
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ENot enough information to decide
Answer
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:
- “Key” means a set of attributes that uniquely identifies rows (tuples).
- “Composite” implies more than one component attribute.
- We do not constrain whether the composite key is primary, alternate, or candidate.
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:
Identify semantic content: “two or more attributes” → composite.Match with definition: composite key = multi-attribute key.No contradictory conditions are present.Therefore, the claim is correct.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:
- Foreign key status is irrelevant to being composite.
- Surrogate keys are artificial identifiers and may be single-attribute; composite does not imply surrogate.
- Normal form level (BCNF, 3NF) is unrelated to the definition.
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