13. The device of claim 10 , wherein the entity extractor is configured to extract the entities from at least one of a text node, an anchor node, an embed node, and an image node of the first web document and the second web document.
14. The device of claim 13 , wherein each of the entities extracted from the text node comprises a text identification (ID) value of a corresponding text, the text ID value generated by combining a node identification (ID) value existing in some nodes of the text node with the corresponding text in first web document and the second web document.