Embodiments of the present invention include generating a facet tree based on words found in one or more documents, the facet tree being a tree data structure that defines hierarchical relationships between a plurality of words. The method may further include calculating a degree of similarity between a first word and a second word based on similarity of usage of the first word and the second word in the one or more documents, and generate a facet tree based on the degree of similarity. The method may further include, for each of one or more candidate words in the one or more documents, calculating a degree of correlation between a co-occurrence of two or more existing facet tree entries in a document and an occurrence of the candidate word in the document, and updating the facet tree on the basis of the one or more degrees of correlation.