A Grammar Base Question Answering Procedure The subject of this paper is a procedure for the automatic retrieval of certain segments of stored information, either explicitly or implicitly represented, through questions posed in natural language sentences. This procedure makes use of a sentence recognition device for the class of grammars which will correctly decide between the grammatical and ungrammatical sentences of a natural language. It is possible to make use of a recognition device of this sort for the following reason: Much data is fully expressible as a set of sentences in a natural language, a set which can be exhaustively and exclusively generated by a grammar. Based upon the rules of this grammar, a sentence recognizer will evaluate sentences, questions in the normal situation. Since the recognition function succeeds just in case the posed question is drawn from the set of sentences expressing the data, or, more correctly, is grammatical in terms of the grammar for this set of sentences, sentence recognition itself is a procedure for retrieving information. When the recognition function succeeds, its value represents the requested information. CACM October, 1967 Rosenbaum, P. CA671006 JB February 27, 1978 2:14 PM 1527 5 1527 1527 5 1527 1527 5 1527 2092 5 1527 2127 5 1527 1155 6 1527 1324 6 1527 1487 6 1527 1527 6 1527 1527 6 1527 1781 6 1527 1856 6 1527