This work presents a methodology for invoice understanding. The invoices of
our domain can be grouped into classes according to their logo. The unders
tanding phase is based on two knowledge levels: a specific knowledge for ea
ch class, called a document model; and knowledge on the whole domain of int
erest, called a domain model. The invoices of a known class are understood
by its document model, while the invoices of an unknown class are understoo
d by using the domain model. The main contribution of this work is related
to the use of the physical and logical constraints of the domain of interes
t for document understanding, without using an OCR system. Our approach has
been tested by some experiments that are intended to identify some regions
within invoices of unknown classes. In most cases, the results have shown
the reliability of the approach.