IBM's Internet Technology Group posted the ninth article in their series entitled Using open source software to design, develop, and deploy a collaborative website. In this article, IBM explains Drupal's database layer, shows module developers how to write portable database code and explains how to install and maintain a module's database schema from one version to another. Last but not least, they show how to add support for their IBM DB2 Express-C database. Sweet!
(Idea: if you are a publisher, get in touch with IBM, and see if you can work with them to make a Drupal book out of their Drupal articles?)