<p>Is there a good object-relational-mapping library for PHP? </p>

<p>I know of <a href="http://www.php.net/manual/en/intro.pdo.php" rel="noreferrer">PDO</a>/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 <a href="http://en.wikipedia.org/wiki/Hibernate_%28Java%29" rel="noreferrer">Hibernate</a> does for Java and NHibernate does for .NET.</p>

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
.