Each database table contains important information, such as field names and sizes, that a COBOL data file does not contain. In order for COBOL to communicate with databases, this information must be written to a separate file, called an Extended File Descriptor (XFD). An XFD typically has the same name as the COBOL data file and resides in the same directory, but its extension is .XFD. When you provide your AcuODBC application, you must include the XFD, along with the executables and any data files.
This chapter describes what information is included in the XFD and how it is mapped to a database format that is easily recognized by your Windows application. It also describes how you can take control of the XFDs using directives. Since this material is relevant during compilation, it applies only to COBOL developers.