23. A method as recited in claim 20 , further comprising receiving user input indicating at least one of a correction and a validation of a line item or header field item of the first document.
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.