This is actually one area where PostgreSQL really shines. With LedgerSMB we define our interfaces in the db (as stored procs) and then have a very simple query

This is actually one area where PostgreSQL really shines. With LedgerSMB we define our interfaces in the db (as stored procs) and then have a very simple query mapper function which looks up the stored procedure in the system catalogs and then figures out the arguments. We have a second function which then generates a query based on supplied args and runs it. No other app code since we started this (at least code in the new framework) includes any SQL. All the SQL stuff is done by one simple function. The real programming is in the database for this interface. Our approach isn't fully developed. I expect we will be working on an object-oriented interface inside PostgreSQL soon which will make the queries look like: SELECT (f).* FROM (select entity(?, ?, ?, ?, ?).save) f; save(entity) will then handle actually saving the data.