4. The method of claim 1 , wherein applying the topic model further comprises: mapping the second semantic class collection to a plurality of documents, each document in the plurality of documents containing the query item; mapping each of the plurality of items in the second semantic class collection to individual words of a plurality of words in individual documents of the plurality of documents; and treating the plurality of topics that are generated as a plurality of semantic classes.
4. The method of claim 1 , wherein applying the topic model further comprises: mapping the second semantic class collection to a plurality of documents, each document in the plurality of documents containing the query item; mapping each of the plurality of items in the second semantic class collection to individual words of a plurality of words in individual documents of the plurality of documents; and treating the plurality of topics that are generated as a plurality of semantic classes. 5. The method of claim 4 , wherein the plurality of words in a particular document are generated by a generative probability process according to a word distribution over topics corresponding to the particular document.