These interfaces provide developers with powerful alternatives to SQL which maintain flexibility and still allow for switching of database back-ends, without requiring any code duplication.

Writing queries explicitly however is not always necessary, as Doctrine performs joins and fetches related objects automatically.

Before long, the community was active and development was receiving regular contributions, among others from the Google Summer of Code project.

The largest influences have been the Java ORM solution Hibernate and the ActiveRecord architecture used in Ruby on Rails.

The purpose of the Doctrine project is to build an equally powerful solution for the PHP language for high-load websites that have to maintain a constant flow of visitors.