Doctrine is an object relational mapper (ORM) for PHP 5.2.3+ . One of the key features of Doctrine is to write database queries in a proprietary object oriented SQL dialect called Doctrine Query Language (DQL), inspired by Hibernates HQL.
Doctrine is one of the best alternatives to SQL that maintains flexibility without requiring unnecessary code duplication. The doctrine requires PHP 5.2.3+ and greater, although it doesn’t require any external libraries. For database function call abstraction Doctrine uses PDO which comes bundled with the PHP.