1. In a computer, a method for establishing topic words to represent a document wherein the topic words are suitable for inclusion in a computer database index structure, the method comprising the steps of: accepting at least a portion of the document from a data input device, wherein the portion of the document includes words; determining a plurality of document keywords from the portion of the document; classifying each of the document keywords into one of a plurality of preestablished keyword classes; and selecting words as the topic words, each said selected word from a different one of the preestablished keyword classes, to minimize an entropy-based cost function on proposed topic words.