Well, internally we're just passing around bits of lisp before building the query. Part of the aim in gathering data through our survey is to get a feel for what data sources people want, so it's likely we'll have more than just SQL. Given that, I don't see why we could just have a homebrew, abstract structure as well, if not the internal representation.

Also, in my distant C# days I was very impressed with Irony, glad it's still around.