Yii includes a database access layer built on top of PHP's [PDO](http://www.php.net/manual/en/book.pdo.php). The database access objects (DAO) interface provides a
uniform API, and solves some inconsistencies that exist between different database applications. Whereas Active Record provides database interactions through models, and the Query Builder assists in composing dynamic queries, DAO is a simple and efficient way to execute straight SQL on your database. You'll want to use DAO when the query to be run is expensive and/or no application models--and their corresponding business logic--are required.
