28. The computer software product according to claim 24 , wherein the instructions, when read by the computer, cause the computer to lower the ranking scores by attributing greater importance to the non-selection of the portion of the refinement options if the user selects another of the presented refinement options, rather than selecting none of the presented refinement options.
24. A computer software product, comprising a non-transitory tangible computer-readable medium in which program instructions are stored, which instructions, when read by a computer, cause the computer to construct an association graph that includes one or more terms as vertices linked by edges, which edges have respective edge scores that represent respective strengths of association of the respective vertices linked thereby; receive from a user a search query that comprises one or more of the terms of the association graph; responsively to the search query, generate, using the association graph, refinement options that comprise respective terms of the association graph, and present information to the user, including refinement options for optional addition to the search query; identify a portion of the refinement options, and corresponding terms, that the user did not select; using the association graph, assign respective ranking scores to search results generated responsively to the search query, including lowering one or more of the ranking scores of the respective search results that are characterized by the non-selected portion of the refinement options, by damping the score of an edge of the association graph between two of the vertices respectively representing two of the non-selected terms; rank the search results according to the ranking scores; and present the ranked search results to the user.