Docs for autoincrement and composite identifiers

manual/docs/Getting started - Record identifiers - Autoincremented.php

+Autoincrement primary key is the most basic identifier and its usage is strongly encouraged. Sometimes you may want to use some other name than 'id'
+for your autoinc primary key. It can be specified as follows:

manual/docs/Getting started - Record identifiers - Composite.php

+Composite primary key can be used efficiently in association tables (tables that connect two components together). It is not recommended
+to use composite primary keys in anywhere else as Doctrine does not support mapping relations on multiple columns.
+<br \><br \>
+Due to this fact your doctrine-based system will scale better if it has autoincremented primary key even for association tables.