As explained before the main reason is to be possible to separate logging database schema and runtime database schema. If each would be tied together using foreign keys, it would not be possible to split them easily. My opinion is that sometimes it's necessary to update database schema manually. For example some databases don't create indexes by default, you need to add them manually, if you need them. You have to try it in your scenario if foreign key adding won't damage anything. I think that it should not. FYI I am not a jBPM developer, so I cannot guarantee that :)