26. The computer storage medium of claim 25 , further comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising: determining the document-categories score based on the degree of match for each document using the association strengths.
25. The computer storage medium of claim 21 , further comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising: mapping one or more of the documents to one or more of the plurality of categories; and associating one or more association strengths to matches between each document and the one or more categories.