1. A computer-implemented method for generating an opinion summary from a document, said method comprising: extracting a plurality of opinion expressions from the document, each opinion expression denoted by an opinion trigger and including an opinion source, opinion topic, opinion polarity and opinion strength; identifying those opinion expressions that share a common opinion source and a common opinion topic; and combining the opinion polarities and opinion strengths of those opinion expressions that share a common opinion source to form an overall opinion summary with one aggregate opinion frame for each common opinion source-topic pairing.