8. A method for searching information based on a digital reference document containing both unstructured and structured information, comprising: performing a plurality of processings, respectively for generating a plurality of types of documents including a fulltext document, a section title document, an info-box document, a category document and a definition statement document, on the digital reference document, to thereby dissect the structured information of the digital reference document, each type of documents including a first field in which a unique identification of said each type of document is recorded, a second field in which a title of a page or of a hierarchical section of the digital reference document is recorded, a third field in which said each type is recorded, and a fourth field in which contents of said each type of documents are recorded; analyzing the fourth field of the generated documents, extracting a plurality of part-of-speech (POS)-based index terms from the fourth field of each generated document, to thereby generate a plurality of document indices for questions and answers that are respectively a fulltext document index, a section title document index, an info-box document index, a category document index and a definition statement document index; extracting document search keywords by receiving a natural language question and analyzing a question pattern, an answer pattern and a question focus from the natural language question; generating a document search result from each of the document indices for questions and answers by performing a document search using the document search keywords on said each of the document indices for questions and answers; extracting an intermediate answer using information about the question pattern, the answer pattern and the question focus from said each of the document search result; and generating a final answer using both the unstructured and structured information in the digital reference document, by integrating and prioritizing the intermediate answers, including assigning different weights to similar intermediate answers in accordance with specificity of each of the similar intermediate answers, wherein the more detailed similar intermediate answer receiving receives a higher weight than a less detailed one, and correlation between a type of each natural language question and each of the plurality of types of documents.
8. A method for searching information based on a digital reference document containing both unstructured and structured information, comprising: performing a plurality of processings, respectively for generating a plurality of types of documents including a fulltext document, a section title document, an info-box document, a category document and a definition statement document, on the digital reference document, to thereby dissect the structured information of the digital reference document, each type of documents including a first field in which a unique identification of said each type of document is recorded, a second field in which a title of a page or of a hierarchical section of the digital reference document is recorded, a third field in which said each type is recorded, and a fourth field in which contents of said each type of documents are recorded; analyzing the fourth field of the generated documents, extracting a plurality of part-of-speech (POS)-based index terms from the fourth field of each generated document, to thereby generate a plurality of document indices for questions and answers that are respectively a fulltext document index, a section title document index, an info-box document index, a category document index and a definition statement document index; extracting document search keywords by receiving a natural language question and analyzing a question pattern, an answer pattern and a question focus from the natural language question; generating a document search result from each of the document indices for questions and answers by performing a document search using the document search keywords on said each of the document indices for questions and answers; extracting an intermediate answer using information about the question pattern, the answer pattern and the question focus from said each of the document search result; and generating a final answer using both the unstructured and structured information in the digital reference document, by integrating and prioritizing the intermediate answers, including assigning different weights to similar intermediate answers in accordance with specificity of each of the similar intermediate answers, wherein the more detailed similar intermediate answer receiving receives a higher weight than a less detailed one, and correlation between a type of each natural language question and each of the plurality of types of documents. 9. The method of claim 8 , wherein the question pattern is one selected from the group consisting of a short-answer type question, a display type question and a descriptive type question, wherein the answer pattern includes a pattern of answers for people, a pattern of answers for organization and a pattern of answers for location, and wherein the question focus is one selected from the group consisting of an entity of interest, an entity property and an entity ID.