I was all ready to reference my soapbox post, then I realized that asurendraz also initiated that topic, so they have heard it before 
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So you’re saying that for your second data provider, you want to create a front-end that dynamically lets the user choose the result columns and conditions, right? While it sounds an awful lot like the built-in query panel, it is possible (within limits) to create a universe-based data provider with code. This post in BOB’s Downloads copies a data provider. A copy of course is creating a new data provider, so you may get some hints from that utility.
Dwayne Hoffpauir 
(BOB member since 2002-09-19)