Is there a good object-relational-mapping library for PHP?
I know of PDO/ADO, but they seem to only provide abstraction of differences between database vendors not an actual mapping between the domain model and the relational model. I'm looking for a PHP library that functions similarly to the way Hibernate does for Java and NHibernate does for .NET.
Look into Doctrine.
Doctrine 1.2 implements Active Record. Doctrine 2+ is a DataMapper ORM.
Also, check out Xyster. It's based on the Data Mapper pattern.
Also, take a look at DataMapper vs. Active Record.