PostgreSQL License Question

First, I want to confirm my understanding that the "without fee" clause in
the PostgreSQL license means that a party may not sell PostgreSQL or works
derived from the PostgreSQL source code.

Second, do loadable PostgreSQL modules constitute a derived work? Can a
party develop new PostgreSQL types or functions and sell them as loadable
modules under their own open or closed source license?

Finally, do applications that install and rely on an unmodified version of
PostgreSQL constitute a derived work?

I apologize if these questions have already been answered on this list,
but I was unable to find them in the archive. Also, please reply to me
directly, I am not subscribed.

Thank you, Ryan Mack