Extended File Descriptors (XFDs) map COBOL records to database fields. These are called XFDs because they're based on standard COBOL File Descriptors (FDs). An XFD file may be created either as a simple text file or as an XML file. In either case, the XFD contains a description of a COBOL indexed, sequential, or relative file based on its fields. XFDs are used to interface to database management systems.