12. A computing system for scoring a discussion thread based on relevance to a query, the discussion thread being in a question-and-answer form, the discussion thread having a post that is the question of the discussion thread and a plurality of posts that are answers of the discussion thread, the computing system comprising: a computer-readable storage medium storing computer-executable instructions comprising: instructions that identify features of the discussion thread, the features including a question-based feature that includes terms relating to the posting of the question of the discussion thread and a combined post feature representing a collection of the terms of multiple answers of the discussion thread; instructions that generate feature scores for the features, wherein the feature score for the question-based feature indicates relevance of the terms relating to the posting of the question of the discussion thread to the query and the feature score for the combined post feature indicates relevance of the terms of the collection to the query; and instructions that generate a relevance score for the discussion thread based on combining the feature scores for the discussion thread; and a processor that executes the computer-executable instructions stored by the computer-readable storage medium.
23. The computing system of claim 12 wherein the computer-executable instructions further comprise instructions that rank a plurality of discussion threads based on their relevance scores and provide the ranking of the plurality of discussion threads.