When your application accesses a data source, it needs to know how to interpret the data that it finds. Your application needs to know about:
To obtain the necessary information, your application reads a data source description. The primary component of a data source description is called a Master File. A Master File describes the structure of a data source and its fields. For example, it includes information such as field names and data types.
For some data sources, an Access File supplements a Master File. An Access File includes additional information that completes the description of the data source. For example, it includes the full data source name and location. You require one Master File and, for some data sources, one Access File to describe a data source.