5. A method for question answering document retrieval which retrieves documents in accordance with a retrieval request in question form, comprising: retrieving associated documents on the basis of a keyword extracted from a question serving as a retrieval request in question form from a user; extracting descriptions associated with the keyword and contained in retrieved documents as first summaries; acquiring document retrieval results including a list of the extracted first summaries; determining a question type of the question by analyzing a semantic role of the question; extracting descriptions corresponding to answers matching the determined question type as second summaries from original-document data, of original-document data stored in an original-document database and forming each document as a retrieval target, which form documents indicated by the document retrieval results; and displaying the document retrieval results and the list of the extracted second summaries, as answers to the retrieval request from the user, on a display device which can be used by the user, the document retrieval results including the list of the acquired first summaries, wherein: the retrieving includes calculating a first score representing a degree of relevance with a keyword extracted from the question for each document when associated documents are retrieved on the basis of the keyword, and selecting, as retrieved documents, the associated documents on the basis of the calculated first scores; and the extracting as the second summaries includes calculating a second score representing a degree of relevance with a keyword extracted from the question for each candidate for a description corresponding to an answer matching the determined question type, and extracting a corresponding description as the second summary on the basis of the calculated second score.
5. A method for question answering document retrieval which retrieves documents in accordance with a retrieval request in question form, comprising: retrieving associated documents on the basis of a keyword extracted from a question serving as a retrieval request in question form from a user; extracting descriptions associated with the keyword and contained in retrieved documents as first summaries; acquiring document retrieval results including a list of the extracted first summaries; determining a question type of the question by analyzing a semantic role of the question; extracting descriptions corresponding to answers matching the determined question type as second summaries from original-document data, of original-document data stored in an original-document database and forming each document as a retrieval target, which form documents indicated by the document retrieval results; and displaying the document retrieval results and the list of the extracted second summaries, as answers to the retrieval request from the user, on a display device which can be used by the user, the document retrieval results including the list of the acquired first summaries, wherein: the retrieving includes calculating a first score representing a degree of relevance with a keyword extracted from the question for each document when associated documents are retrieved on the basis of the keyword, and selecting, as retrieved documents, the associated documents on the basis of the calculated first scores; and the extracting as the second summaries includes calculating a second score representing a degree of relevance with a keyword extracted from the question for each candidate for a description corresponding to an answer matching the determined question type, and extracting a corresponding description as the second summary on the basis of the calculated second score. 6. The method according to claim 5 , wherein the displaying includes deciding a display order of the extracted first summaries on the basis of the first scores corresponding to the documents containing the first summaries, and deciding a display order of the extracted second summaries on the basis of the second scores corresponding to the second summaries.