ActiveRecord takes the last part of the class name
after the underscore like Phprojekt_Test
is mapped to the database table name test.

Upercase characters are translates to a underscore.

The table name is always lowercase.
So Phprojekt_TestInstance is mapped to the database table
test_instance as well as Projects_Model_TestInstance would do. 

Foreign keys, like a project that has many todos
must be the name of the table in lowercase concated with „_id“.
E.g. if Phproject_Project has many Phprojekt_Todo
in the todo table the must be a column called project_id.