For those who want to take this kind of approach (object prevalence) in Common Lisp see http://common-lisp.net/project/cl-prevalence/

Sven Van Caekenberghe (the author of cl-prevalence) and I used this approach to power the back-end/cms of a concert hall back in 2003. A write-up of our experiences can be found at http://homepage.mac.com/svc/RebelWithACause/index.html

The combination of a long-running Lisp image with a remote REPL and the flexibility of the object prevalence made it a very enjoyable software development cycle. It's possibly even more applicable with the current memory prices.

I especially liked the fact that your mind never needs to step out of your object space. No fancy mapping or relationship tables, just query the objects and their relations directly. I guess that's what SmallTalk developers also like about their programming environment.