Using Directives

Directives are optional comments that you can use in your FDs to control how things look in the XFD file. Many applications will not use directives at all. They're most commonly used when a site intends to do a lot of work with a database management system outside of the COBOL application, and wants to control how the database table is built. They are also used to customize how fields are displayed by the record editor, alfred.

Directives are special comments placed into an FD in your COBOL source code. They guide the building of the data dictionaries, which in turn guide the building of the database table (and the display of data in the record editor).

Each directive includes the letters XFD. These three letters indicate to the compiler that the comment is to be used in data dictionary generation.

Directives offer you a great deal of control over how the XFD file is built. Among other things, they enable you to:

• specify a field name to be used in the XFD, in place of a COBOL field name
• map elementary items of a group item together into a single field
• cause numeric COBOL data to be treated as a text string in the XFD
• cause the fields from a specific record in a file to appear in the XFD (rather than just the fields from the largest record)
• mark specific fields as candidates for a secondary database table, if all of the data will not fit into a single table
• cause a fixed-length field to be designated as variable-length
• assign a column the DATE type, so that it will have the built-in functionality that dates have in an RDBMS
• give a name to the data dictionary file itself
• include comments in XFD files

Directives are always placed within a COBOL FD. They do not affect Procedure Division I/O statements, and they do not change your COBOL fields in any way. Rather, they guide the building of the data dictionaries, giving you a measure of control over the way COBOL data is mapped to XFD fields.