For a serializable schedule, precedence-graph vertices represent transactions and directed edges represent conflicts. Which vertex ordering yields an equivalent serial schedule?
A conflict edge Tᵢ→Tⱼ requires transaction i before transaction j. A topological ordering respects every edge of the acyclic precedence graph and gives the conflict-equivalent serial order. DFS/BFS visitation and numeric labels need not respect those edges. Thus A; this graph criterion concerns conflict serializability.
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