In Rails, say a blogging application, given a particular post object you could get the name of the author of the post doing something like:
post = Post.find(1)
author_name = post.author.name
Is there a PHP equivalent using DataObject, something like (just making up imaginary syntax here):
$postsTable = DB_DataObject::factory('posts');
$authorName = (($postsTable->id = 1)->find(true))->author->name;
| finds and autofetches post #1 |->author->name
If you want an ORM with an API like that I would recommend PHP ActiveRecord:
http://www.phpactiverecord.org/projects/main/wiki/Finders
You may also be interested in Propel ORM:
http://www.propelorm.org/wiki/Documentation/1.6/Relationships