6. The method of claim 4 , further comprising: computing a score for an expanded query in the query feature index when compared with the received query based on a weighted sum of levels of similarities per each feature, wherein the levels of similarities are computed using the weightings of the features of the expanded and received queries.
6. The method of claim 4 , further comprising: computing a score for an expanded query in the query feature index when compared with the received query based on a weighted sum of levels of similarities per each feature, wherein the levels of similarities are computed using the weightings of the features of the expanded and received queries. 9. The method of claim 6 , wherein selecting the one or more advertisements comprises, for each potentially-related advertisement for mutual comparison: weighting ad features within the advertisement according to a weighting scheme to produce a weight for the advertisement; increasing the weight of the advertisement if its title closely matches the received query; and creating a final advertisement score based on a weighted sum of dot products between feature types of the expanded received query and those of the advertisement and any increased weight of the title of the advertisement.