22. A method as recited in claim 20 , further comprising generating an alert upon encountering a potential problem when determining the validity of the first document, wherein the alert includes identification of a mismatch in expected similar or identical values in the first and complementary documents.
20. A method, comprising: determining a validity of a first document by simultaneously considering: textual information from the first document, textual information from a complementary document, and predefined business rules; at least one of: correcting OCR errors in the first document, and normalizing data from the first document prior to determining the validity, using at least one of the textual information from the complementary document and the predefined business rules; and outputting an indication of the determined validity.