SYNONYM EXTRACTION DEVICE, SYNONYM EXTRACTION METHOD, AND SYNONYM EXTRACTION PROGRAM

A synonym extraction apparatus determines, for compound words included in the document, that types of nouns constituting the compound word are each a Sahen-noun or a noun other than a Sahen-noun to determine a pattern of a sequence of the types of the nouns constituting the compound word. The synonym extraction apparatus then extracts a group of compound words having an identical pattern of the sequence of the types of the nouns described above from the document, and then extracts compound words having an identical leading or ending word from among them. Next, the synonym extraction apparatus creates, for a group of compound words having the identical pattern of the sequence of the nouns and the identical leading or ending word, a co-occurrence vector having, as a component, a noun appearing in the same sentence as the corresponding compound word, and outputs, as synonyms, a group of compound words having a degree of similarity between the co-occurrence vectors of the compound words equal to or greater than a predetermined threshold.