When you save a Master File, you must also create a corresponding empty data source that will hold the data for the fields defined in the Master File. This data source is saved in the application directory.
After creating the empty data source, you can load data into it with a MODIFY request, or a Maintain request. After you populate the data source, you can use it in conjunction with the Master File in a report request.
The Master File opens to the Field View tab in the Synonym Editor.
FOCUS creates an empty data source (.foc) in the background.
The .foc file is stored in the application directory.