I created a video, showing how to calculate discount using Pentaho PDI and the Business Rules Maintenance Tool.
Again, the idea is to externalize the rules and to not have the rule logic inside the transformation. This way - if the rules change - the transformation does NOT need to change. It's also a clear devision of responsibilities: IT cares for the transformation and the business about the rules.
There is no coding involved when writing rules and constructing complex rules logic. The web application allows to maintain projects, rules, actions, user roles, import/export projects and more.