Information classification tasks require sorting records into one or more categories, usually based on the comparison of document features to category definitions. Classification systems combine human expertise and machine learning techniques to meet users' performance requirements, while dealing with the constraints imposed by the documents and definitions. Syndromic surveillance identifies potential outbreaks of health problems such as Gastro-Intestinal illnesses by classifying patient records that are likely to represent a patient with that illness. Legal discovery identifies letters, email, and other documents that are likely to be relevant to a specific legal matter. Human expertise is an expensive and valuable resource.