25. A method as recited in claim 20 , wherein determining the validity of the first document includes automatically correcting values for expected or actual line items or header field items in the first document based on at least one of the textual information from the complementary document and the business rules.
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.