I've been working on a plugin for a while. But now I wanted to extend the product model in order to maintain the modulairity. Sadly I can't find any documentation on how to extend existing models in a plugin/module.
So I have two questions. First I'd like to know how to extend core models (like category and product) by a plugin/module. The second thing I'd like to know is how can I update the complete database with all sql files that are located in the Thelia system by using Propel.