DQL (Doctrine Query Language) is a object query language which allows
you to find objects. DQL understands things like object relationships, polymorphism and 
inheritance (including column aggregation inheritance).
<br \><br \>
So instead of writing lots of SQL inner and outer joins, unions and subselects yourself,
you can write simple DQL queries where relationships are being referenced with dot-notation.
<br \><br \>
You can execute DQL queries with Doctrine_Connection::query() method.