I'm in search of a web API framework.

I'm not interested in building web clients on the server. Why should the client logic reside on the server? That makes no sense.

FRAPI II
http://getfrapi.com/

FRAPI is many steps in the right direction, but too limited.

I want something like PURE for the API where I can define a directive which maps to a data structure.

One benefit to this is I can provide the developer with a structure quite a bit flatter than the database model (and for that matter, perhaps SQL isn't the premier option for web mashups).

Another benefit is I can define what's public very easily.

The solution would be implemented on both the I and the O of I/O. Perhaps some values are not publicly visible, but they are publicly writable (and more commonly the reverse). A directive also provides validation. The hash could map a value's name to the function which validates it.