Let's say I have a website, where any person can buy and sell items and 2 registered users can send messages to each other regarding a product. One of the relations in my database is:
idMessage| Sender| Recipient | idObject| Subject
1 | userA | userB | #1234 | size
2 | userB | userC | #1234 | discount
So, the question should be, is there a transitive functional dependency? if the answer is yes, then this is not a 3NF.
Not sure if I completely understand the
idObject attribute, but if [idMessage] determines [idObject] via [Recipient] or [Sender] then we have a transitive functional dependency hence this would not be a 3NF. If [idObject] is determined by the [idMessage] attribute then all non-key attributes are fully functional dependent only on the primary key [idMessage] and this would be a 3NF.
You may want to add some explanation on What is
Hope this helps.