Abstract: Systems (100) and methods (500) for searching electronic documents. The methods comprise: using first electronic documents to derive topics respectively defined by sets of words; using the topics to transform a format of known subject reviews and written pieces from a textual format to a numerical format in which each of the subject reviews and written pieces is expressed as a topic vector containing a plurality of first numbers respectively corresponding to the topics; generating concept vectors by transforming a domain of the topic vectors from a first numerical domain to a second different numerical domain; and determining similarities between the known subject reviews and the written pieces by comparing first concept vectors that are associated with the known subject reviews to second concept vectors concept vectors that are associated with the written pieces.