Hi Jay,
ByD provides a documentation for every data source (incl. custom data sources).
Just open work center "Business Analytics" and view "Data Sources", search the data source of your choice and click on the icon in column "Documentation". As result you will get a documentation of the data source incl. a list of fields.
For ByD standard data sources you find documentations on the SAP Business Center (logon required):
Characteristic Indexes Documentation
Best regards,
Knut