If accessing existing data in a relational database, you need to know how to declare your data to match the database fields.
If your COBOL code isn't written yet, you should follow the guidelines given in the Appendix for your specific RDBMS.
If your COBOL code already exists, you can make necessary adjustments by adding XFD directives to your code. XFD directives are comments that guide the creation of the eXtended File Descriptors (XFDs). The XFDs in turn help map the COBOL fields to their equivalent database fields. XFD directives are described in Using XFD Directives, and XFDs are described in XFDs.