Topic: Flex your model?

Model composition
Do people combine their models into composites ever (OO Composition)?  Maybe it would be nice to define a higher-level model that uses underlying models, but doesn't have a database table backing itself.  Anyone?  How did it work out for you?

Non-data backed Models
Do people make models that are not backed by database tables at all? (not even via OO composition).  Are there any interesting use-cases for sticking business logic into an object for abstraction?

Alernative data backed Models
This one I think I've seen mentioned before, but do people make non-database data-backed models, that say -- break out and return the content of a directory?  Or maybe report back the CPU load, disk usage, etc?  That would go into a Model, right?  Just wondering... smile