Paper - II (xi) — Database Management System MCQ — 44 Practice Questions with Answers

Explanation

The candidate keys are AB and AC: AB determines C directly, and AC determines B through C -> B. Thus A, B, and C are all prime attributes. The dependency C -> B has a determinant that is not a superkey, so BCNF is violated, but its right-hand side B is prime, so 3NF is satisfied. A BCNF split into CB and AC is lossless on C, yet AB -> C is not derivable from the projected dependencies alone.

Explanation

In a multicolumn B-tree, the leading column matters most for ordered search. Equality on district_id narrows the first segment of the index, and a range on exam_date can then be scanned within that segment; predicates that begin from the second or third column are weaker matches.

Explanation

Under 2PL, each transaction has a growing phase for lock acquisition and a shrinking phase after it starts releasing locks; this guarantees conflict serializability. However, basic 2PL does not require write locks to be held until commit. Strict 2PL adds that discipline for exclusive locks, which prevents dirty reads and cascading aborts, but deadlocks still remain possible.

Explanation

A safe relational calculus query must produce a finite result determined by the active domain of the database. In {t | not Student(t)}, the free variable t is not positively range-restricted by any relation. It may denote arbitrary tuples that do not occur in Student, making the result unbounded and not equivalent to a finite relational algebra query.

Explanation

Write skew occurs when transactions read overlapping data, update different rows, and together break an invariant even though neither overwrites the other. Serializable isolation is the standard-level guarantee that concurrent execution has an equivalent serial order, so one transaction must be blocked or aborted in such a conflict pattern.