Differenciating Invoices and Bills

[Nestor Stura]

Hi all,
I am building some reports based on business tables, with MSAccess and SQlite3.
I have the following doubt, Client's invoices and Vendor's bills are
kept on the same table, I could  not find any field that differentiate
both.
Is there any way in this table to split them or should I access via
Customers and Vendors tables?
Thanks for any help.
Néstor