1. A computer-implemented method comprising using at least one processor 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.
3. The method of claim 1 , wherein the key phrase is one of a plurality of key phrases being identified during the search of the set of documents, the plurality of key phrases are ranked according to a polarity criterion, the polarity criterion identifying a word indicating sentiment, and each document in the first subset of documents includes a key phrase ranking higher than a threshold value.