1. A computer-implemented method for finding a target document in a spoken language processing, the method comprising: calculating, using a processor, a score of each document in a document set, in response to a receipt of first n words of output of an automatic speech recognition (ASR) system, wherein n is greater than or equal to 0; reading a prior distribution of each document in the document set from a memory device; updating, for each document in the document set, the score, using the prior distribution and a weight for interpolation, wherein the weight for interpolation is calculated based on a confidence score of output of the ASR system; and finding a target document among the document set, based on the updated score of each document.