This chapter will note that Drupal is described as being “database agnostic”, as the code strives to not depend on the underlying database that is being used. It will review the database abstraction layer, and will talk about the currently supported databases. It will detail how in spite of this noble aim, MySQL is still strongly favored. It will compare MySQL support with PostgreSQL support. Finally, it will offer a preview of the database layer rewrite that is happening for Drupal 7, detailing how this may finally make Drupal database agnostic.

1. Abstraction Layer Design
   1. Abstraction Concepts
   2. MySQL Support
   3. PostgreSQL Support
2. Database Abstraction in Drupal 7