9. The method according to claim 1 wherein the preestablished keyword classes have an ordering of classes, and an arbitrary word in one of the preestablished keyword class is expected to appear substantially no more frequently in an information domain than any arbitrary word in an immediately preceding keyword class.
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.