Annotation advice appreciated

Hey guys,
I'm currently making a plugin, a sort of casting plugin where people can submit a project, others can show their intrest and the project owner can pick interested users and set them as a collaborater (this adds a relationship with the collaborator and the project).

When the project is finished the owner can fill in a review on their collaboration and upload a result.

at the moment I list all the collaborators in the review page and the owner can rate the collaborators, this happens with an annotation made on the collaborator.
The review itself is an object linked to the original project page.

Annotate the collaborators is nice, but the annotation entity guid is of course the collaborator, the namestring is collaborationrate for instance, the valuestring is the rating int. and the owner guid is the projectowner. do I link this with the review itself? Should I set the owner_guid of the annotation to be the object instead of the rater? Is that the best approach? I could fetch the rater then by getting the owner_guid of the owner_guid, but this all seems a bit of a hassle to me.

Or should I make an entity of each rating? That looks overkill to me as well, since it's just that where annotations are made for.

Maybe someone has an example how another plugin handles this.
Annyway, thanks