Patent ID: 8712977

Claim:
A computer-readable recording medium storing therein an information retrieval program that causes a computer to execute, with respect to content consisting of files, a retrieval process in which files to be retrieved are narrowed down by using a bit string for each character in the files to find characters making up a retrieval keyword to retrieve a keyword identical to or related to the retrieval keyword in the files to be retrieved, the bit strings being indicative of the presence of the characters in the files, the information retrieval program causing the computer to execute: acquiring an appearance rate representative of a rate of files that include the character to be compressed among the files to be retrieved; extracting, from among the bit strings, a bit string of an arbitrary character having the acquired appearance rate; extracting, from a Huffman tree group having a plurality of types of special Huffman trees, a special Huffman tree corresponding to the acquired appearance rate, each type of special Huffman tree having a different number of bits of special symbol strings, the special Huffman tree having leaves of a plurality of types of symbol strings covering patterns represented by a predetermined number of bits and a special symbol string having a number of bits greater than the predetermined number of bits; and compressing the extracted bit string, by using the extracted special Huffman tree, wherein a range of appearance probability is divided into areas according to the special Huffman trees, and when an appearance probability identified by a divided area of a first special Huffman tree is set lower than an appearance probability identified by a divided area of a second special Huffman tree having a leaf of a special symbol string having a number of bits greater than the special symbol string of the first special Huffman tree, the extracting of the special Huffman tree includes extracting the special Huffman tree belonging to the divided area including the appearance rate.