At the heart of the Acu4GL database product are the data dictionaries that map COBOL records to database fields. These dictionaries are also called eXtended File Descriptors (XFDs) because they're based on standard COBOL file descriptors (FDs).
XFDs are used by Acu4GL to interface to database management systems. They are also used by Alfred, Acucorp's record editor and European character mapping in Acuconnect and AcuServer.