1. A relevancy ranking method comprising the steps of: parsing an input query into at least one query predicate structure; parsing a set of documents to generate at least one document predicate structure; comparing each of said at least one query predicate structure with each of said at least one document predicate structure; calculating a matching degree using a multilevel modifier strategy to assign different relevance values to different parts of each of said at least one query predicate structure and said at least one document predicate structure match; and calculating a similarity coefficient based on pairs of said at least one query predicate structure and each of said at least one document predicate structure to determine relevance of each one of said set of documents to said input query.