What Is a Data Source Description?

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:

• The overall structure of the data. For example, is the data relational, hierarchical, or sequential? Depending upon the structure, how is it arranged or indexed?
• The specific data elements. For example, what fields are stored in the data source, and what is the data type of each field (character, date, integer, or some other type)?

To obtain the necessary information, your application reads a data source description, also called a synonym. The primary component of a synonym 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.