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  1. GATE CS
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  3. Databases

A prime attribute of a relation scheme R is an attribute that appears A. in all candidate keys of R B. in some candidate key of R C. in a foreign key of R D. only in the primary key of R

GATE 2014 · Databases · Candidate Key · easy

Answer: B. in some candidate key of R

  1. State the formal definition: A prime attribute is one that participates in at least one (some) candidate key of the relation. This is the standard textbook definition used in normalization (2NF, 3NF analysis).
  2. Evaluate all options: Option A: 'in all candidate keys' — too restrictive. An attribute is prime if it is in even one candidate key, not necessarily all. Option B: 'in some candidate key' — this exactly matches the definition. Correct. Option C: 'in a foreign key' — foreign keys have no relation to the prime/non-prime distinction. Option D: 'only in the primary key' — primary key is just one chosen candidate key; an attribute in any other candidate key is also prime.