I have the following requirements (as part of a larger system).
In the database, I need to maintain a list of
suppliers who sell those parts.
suppliers can sell the same
part and each
part can be sold by many suppliers. However, the prices vary.
In my system, I should be able to keep track of the one, and only one,
supplier we purchase a specific
The way I figure it, I need two relationships on the entities
Part. One relationship
Sells recording that the particular
supplier carries the particular
part and vice versa, and another relationship
Purchase that records who we purchase an
However, I don't record the attribute
price, twice. I think that would be bad practice. Therefore, I ask, can I relate one relationship to another?
I've included a sample diagram below. The dashed line is what I'm not sure about.