As described in http://moodle.org/mod/forum/discuss.php?d=110362
I post here the same request.

I built a database with 10 fields.
Eight of them are for remote users, they are supposed to fill them.

Two of them need to be filled ONLY by the course teachers.
Is there a way to restrict the access to these two "special" fields?

What I am asking is a database field level view/read/write permission to assign only to specific roles.

The same feature should be implemented by managing more than one form to add records to the database.
If I had two different input forms, I would assign one form to teachers and one to students by role.
This would be great.