A method is provided that includes specifying enabling relationships, which map enabling sets of one or more enabling attribute-value pairs to respective enableable attributes. Responsively to the search query, a current state is designated that comprises current-state attribute-value pairs, and a result set is generated containing some of the items of a corpus. An enableable attribute of one of the enabling relationships is identified as enabled when the current-state attribute-value pairs include all of the enabling attribute-value pairs of the enabling relationship. A populated attribute-value pair is found that comprises the enabled attribute and a value therefor, and which, when added to the search query, results in an extended query that is satisfied by at least one of the items in the corpus. The result set is presented in association with the value of the populated attribute-value pair as a refinement option. Other embodiments are also described.