Data inside CAPITAL is held in fairly generic DBF version 3 files. I believe there is an ODBC driver that comes with Microsoft Office for FoxPro 2.7 which you should be able to use for read only access. You may have an ODBC or similar interface that can read these files natively in your development language. The smaller versions of CAPITAL do not come with API type software.
An ActiveX/OLE server will also be available for purchase from CAPITAL Office Business Software shortly.
Because you can export data in any format you want there is no such thing as a 'standard' catalog file in CAPITAL.
You can also use the report writing tool that comes with CAPITAL called Visual Builder, to generate a text file which might be a catalog, customer list, etc. The only issue here is that the report would have to be run periodically in order to refresh the text file that is generated.