When your application accesses a data source, the application needs to know how to interpret the data that it finds. To accomplish this, the application reads a synonym, which is an Information Builders term for the generated metadata associated with the particular data source.
Your application needs to know:
The synonym provides an alias for the data source that tells the server how tables are described and where to find them.
The primary component of a synonym is a Master File. The 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 types of data sources, an Access File supplements the 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. The nature of the information in the Access File is specific to each data source. You need one Master File and for some types of data sources, one Access File to describe a data source.