The forth video of the six.

Adenda

Part 4: Open process, open framework, and open language
4-1: Agile as an Open Process
4-2: Rails, a web application framework
4-3: Unit testing and testing frameworks
4-4: Ruby as a DSL
4-5: A predicatable change is not a change.
4-6: Convention over Configuration, or Rails application as a big configuration file.