I'm evaluating the possibility to write some custom transformations or
jobs for Kettle.

I've been able to download the source code from SVN and I've
successfully compiled it.

Now, I'd like to get some developer documentation, but I found very
few information ([1], [2] and [3]). It would be very helpful if you
can provide some links about the following topics:

- General Kettle architecture
- How to write your own jobs and transformations (relevant interfaces
and methods), and how is data exchanged between them, at the API

If such documentation does not exist, it would be enough to know the
relevant interfaces and the name of some simple classes implementing

Thanks in advance,