The Doctrine Project is a collection of open source libraries and tools for dealing with database abstraction and Object-Relational Mapping written in PHP.

The Doctrine Project is a collection of open source libraries and tools for dealing with database abstraction and Object-Relational Mapping written in PHP.

Doctrine 2

When we say Doctrine 2 it usually refers to Doctrine ORM Project. The ORM sits on top of the database abstraction layer (called DBAL). It also uses Doctrine Common (which provides extensions to core PHP functionality).

Side projects

Then you have side projects dedicated to some DBMS which provide transparent persistence for PHP objects:

Documentation

Doctrine 1

The first version doesn't have a separate project for the relational mapper and the database abstraction layer. It requires PHP 5.2.3+ and the latest version is 1.2.4.