I came across the same problem recently. I wanted a thin layer to turn my SQL database into a webservice with JSON or XML support. All I wanted to do was to have to write the SQL statements... it seemed a pretty reasonable thing to ask.
However, all the options I found involved installing some sort of enterprisy "do everything" solution. So I ended up writing some "glue" which took SQL statements defined in XML "dataset" definitions, and served a simple, RESTful web service.
I documented my approach here:
http://www.nsquared.co.nz/jarvis-docs/jarvis_guide.odt
If you want to use the framework, I can give you a tarball of the latest release. It's used in three or four small applications currently, 2 ExtJS, 1 Flex, and 1 Asp.Net.
