Several elements of COBOL require special handling when XFDs are built. These include multiple record definitions REDEFINES, FILLER, and OCCUR. This section describes how the Compiler handles each of these situations.
Note that in many instances you can override the default behavior described below by placing special comment lines in the FDs of your COBOL code. These comments are called XFD directives, and are described in the chapter "Using XFD Directives." For example, the WHEN XFD directive allows you to use multiple definitions for a single set of data by specifying when each definition should be used.
Databases generally do not support the notion of multiple definitions for the same column. As the following paragraphs explain, whenever a COBOL program gives more than one definition for the same data, the Compiler makes a choice about which definition to use in the XFD. Then it disregards the rest.