1. A computer implemented method for extracting keyphrases from natural text, characterized in that it comprises: (a) generating one or more phrases in the natural text based on one or more phrase separators in the natural text, wherein each of the one or more phrase separators comprises one or more words from the natural text; (b) assigning a weight to each of the one or more phrases in the natural text based on its frequency in the semantic frames of one or more sentences of the natural text, wherein each of the one or more sentences is divided into one or more sub-texts by the one or more phrase separators, and the assigned weight is calculated for each of the one or more phrases based on a frequency of the respective phrase within the one or more sub-texts of each sentence; and (c) ranking the one or more phrases based on their weights to extract one or more keyphrases having the highest ranks.