17. A non-transitory computer-readable medium to identify topics among a group of documents, comprising a set of instructions which, when implemented by one or more computing devices, cause the one or more machines to perform the following operations to: search a set of documents to identify a key phrase, the identifying comprising clarifying a term found in at least one of the set of documents by extracting log data related to the term from a corresponding session log of a user interaction with a service or product, the clarifying relating the term to the key phrase; select a first subset of documents from the set of documents, based on each document in the first subset of documents including the key phrase; build a syntactic tree of a sentence within a document from the first subset of documents, the syntactic tree identifying a relationship between parts of the sentence; build a lexical pattern including a plurality of tokens, the plurality of tokens including a key phrase token, a polarity token, and a special token that indicates a relationship between the key phrase token and the polarity token, the special token being separate and distinct from the key phrase token and the polarity token; and determine that the document conveys an opinion by matching the lexical pattern including the plurality of tokens to the syntactic tree.
18. The computer-readable medium of claim 17 , wherein the set of documents are from an electronic community forum related to a product available through an electronic commerce system.