1. A method for web documents clustering, comprising: inputting a plurality of web documents; collecting link information and directory structure information of the inputted web documents; extracting, by a processor, according to the collected link information and directory structure information, a hierarchical structure for the plurality of web documents; after extracting the hierarchical structure, revising the extracted hierarchical structure by analyzing the link information in the inputted web documents; and generating and outputting, based on the extracted hierarchical structure, plurality of clusters of the plurality of web documents, wherein the directory structure information is extracted by comparing directory paths of the web documents, wherein the directory paths include information about a location in a web server where each of the plurality of web documents are stored, and the extracted hierarchical structure corresponds to ancestor-descendent relationship structure of the plurality of web documents, wherein the plurality of web documents are grouped into the plurality of clusters according to the extracted hierarchical structure such that a first web document of the plurality of web documents and descendent web documents of the first web documents are grouped as a first cluster of the plurality of clusters, and a second web document of the plurality of web documents and descendent web documents of the second web documents are grouped as a second cluster of the plurality of clusters, and wherein the first and the second clusters have an ancestor-descendent relationship between each other corresponding to the extracted hierarchal structure.
3. The method according to claim 1 , wherein extracting the hierarchical structure comprises: determining a first hierarchical structure according to the collected directory structure information; determining a second hierarchical structure according to the collected link information of the web documents; and combining the first hierarchical structure and the second hierarchical structure to determine the extracted hierarchical structure.