Appropriate ness (Appropriation?)

I recently did a constraint-satisfaction problem (CSP) in LISP to solve sudoku puzzles. I finally was able to visualize the recursive pattern and (to me) it looked alot like the stock market circa 1998-2005 -- up-down-up-down-down-up-up-down-down-down-down-up-up-down-up-up...

This actually reminded me of Matt Zandstra's book PHP 5 Objects, Patterns, and Practice. I read this at a time in my life where I had (naively) written an architecture for a system (in PHP5) which was quickly becoming unmanageable. This book helped me collect my thoughts about how to re-collect my code.

One of the things that I found very interesting which had never blipped on my radar was the idea of the appropriate throwing, catching, handling, and re-throwing of exceptions. Matt Zandstra emphasized that exceptions are powerful error-recovery tools -- but that they need to be handled at the appropriate level in your application: that model-level exceptions must be caught and handled (hopefully recovered) in the model and -- only when necessary -- passed controller. Heaven forbid if they propagate to the view.

Chris Snyder's book Essential PHP Security chimes in with the idea that often errors which occur at lower levels can cause security breaches. How many sites have you visited that have said "Cannot select `id` from table `users` with value ....". So if i just tweak this input-field...

So think about exceptions and their course through your application -- are there some which are relevant only to the model? Or are some worthy of propagating all the way up to your controller? Who owns that exception? Where does the buck stop?