Just one addition,
if you are using only 1 flat file, you can create a ODBC connection & in File DNS define ODBC Text Connection. this connection can be used for an universe to be created using flat file.
creating a universe for just a single flat file, as per my knowledge & experience, doesn't make sense. because you will need different dimensions, fact tables & creation of which from single file is very tedious job. Apart from that Analytical reports are used for aggregated OLAP data that is huge in amount & 1 text or cvs file containing this data sounds practically imposible.
if you want to use that file for reports, you can simply call it in BO Reporter when you are defining Data Provider & use it's data.
hope, i have not created lot of ambiguity.
Cheers,
Pat.