A query suggestion to expand an initial query is calculated whereby the cost of the expanded initial query is bounded in both time and quality. The user validates a subset of the top-n answers Q(G) to a query Q and provides adjusted configuration parameters. The top-n diversified δ-expansion terms Q′ are calculated from the validated subset of answers Q(G) to the query Q and are provided to an interactive user interface for selection. Answers Q′(G) for the top-n diversified δ-expansion terms Q′ are cost bounded by cost threshold δ and exploration range r specified by the user. The user selects a new term of terms Q′ and an incremental query evaluation of the new term is invoked to compute expanded query answers Q′(G) by incrementally updating the validated subset of answers Q(G), without re-evaluating an expanded query Q′ including the new term from scratch.