When position 17 is left blank, the name specified in positions 19 through 28 is a field name.
You cannot specify field names if you specify the FORMAT keyword.
Physical files require that each field be named. These names must be unique within the record format. The field names appear in the physical buffer in the same order as they are specified in the DDS.
If you are describing a simple or multiple format logical file, you can use the record format as it exists in the physical file on which this logical file is based, and you do not need to specify field names.
If you do not use the record format as it exists in the physical file, you must name each field specified in a logical file. In a simple or multiple format logical file, each field name must be unique within the record format and must correspond to a field in the physical file record format. The field name order is the order in which the fields appear to programs using the logical file.