1. A system comprising: a communication module, implemented using one or more processors, that is configured to receive a selection, over a network from a client machine, that identifies a filter, the filter including a first attribute-value pair, the first attribute-value pair including a first attribute and a first value, the first attribute-value pair being included in a concept query that was extracted from a query including at least one keyword that was received over the network from the client machine; and a search engine, implemented using one or more processors, that is configured to identify a plurality of filters responsive to receipt of the selection, the identification of the plurality of filters is based on the first attribute and probabilities describing occurrences of attribute-value pairs in a plurality of listings that respectively describe items that were previously transacted on a network-based marketplace, the plurality of filters including a plurality of values, the communication module is configured to generate a user interface including the plurality of values and search results that are identified based on the concept query, and to communicate the user interface, over the network, to the client machine.