5. A computer-implemented method comprising: selecting one or more index terms from a plurality of index terms; identifying one or more documents of a plurality of documents to which each of the one or more index terms has been assigned; comparing, for each of the one or more index terms, each of the identified documents to a specific document; determining a score for each of the one or more index terms based on the comparing; assigning the index term associated with the highest score to the specific document; selecting a first category; selecting one or more second categories assigned to a first supercategory; comparing the first category and the one or more second categories; computing a first score for the first supercategory based on the comparisons; selecting one or more third categories assigned to a second supercategory; comparing the first category and the one or more third categories; computing a second score for the second supercategory based on the comparisons; assigning the first category to the first supercategory when the first score is higher than the second score; assigning the first category to the second supercategory when the second score is higher than the first score; wherein the comparing of each of the identified documents to a specific document and the comparing the first category, comparing of the first category and the one or more second categories, comparing the one or more second categories, and the assigning the index term associated with the highest score to the specific document each include computing a likelihood ratio.
5. A computer-implemented method comprising: selecting one or more index terms from a plurality of index terms; identifying one or more documents of a plurality of documents to which each of the one or more index terms has been assigned; comparing, for each of the one or more index terms, each of the identified documents to a specific document; determining a score for each of the one or more index terms based on the comparing; assigning the index term associated with the highest score to the specific document; selecting a first category; selecting one or more second categories assigned to a first supercategory; comparing the first category and the one or more second categories; computing a first score for the first supercategory based on the comparisons; selecting one or more third categories assigned to a second supercategory; comparing the first category and the one or more third categories; computing a second score for the second supercategory based on the comparisons; assigning the first category to the first supercategory when the first score is higher than the second score; assigning the first category to the second supercategory when the second score is higher than the first score; wherein the comparing of each of the identified documents to a specific document and the comparing the first category, comparing of the first category and the one or more second categories, comparing the one or more second categories, and the assigning the index term associated with the highest score to the specific document each include computing a likelihood ratio. 9. The method of claim 5 , wherein the likelihood ratio is a log likelihood ratio.