Patent ID: 7418443

Claim:
A question answering system comprising: a CPU; a question answering unit that executes search processing on a basis of an input question and acquires answer candidates to the question; an analysis unit that executes syntactic analysis processing or syntactic and semantic analysis processing on a passage obtained as a result of the search processing executed by the question answering unit to generate an analysis result holding a case relation between words of the passage to be analyzed; a tree structure generation unit that generates a tree structure based on predicate-argument structure explicitly expressing the case relation on a basis of the analysis result of the analysis unit; a feature extraction unit that extracts a relation between a search word applied in the search processing executed by the question answering unit and each acquired answer candidate as a feature corresponding to each answer candidate from the tree structure generated by the tree structure generation unit; an evaluation unit that determines an evaluation value of each answer candidate on a basis of the feature extracted by the feature extraction unit; a re-ranking unit that re-ranks the answer candidates on a basis of the evaluation values determined by the evaluation unit; a tree structure database that stores data of the tree structure generated by the tree structure generation unit in association with the passage based on which the data of the tree structure is generated; and a passage search unit that executes search processing of the tree structure database on a basis of the passage input from the question answering unit, the question answering unit, analysis unit, tree structure generation unit, feature extraction unit, evaluation unit, re-ranking unit, and passage search unit being executed by the CPU, wherein if the search processing executed by the passage search unit finds a passage in the tree structure database, the tree structure generation processing executed by the tree structure generation unit is skipped and the tree structure stored in association with the passage found from the tree structure database is used.