Impossible relationship ??

Is it possible to establish a relationship between a "simple" text field (which has only one value) and a text field, which takes values from a list using an option box?

Example:

Contract :: Specialty (which can only have one of the values 1,2,3,4 or 5)

That should relate to

Supplier :: specialty (s) (can have 1, 2 3, 4 or 5 values in it.

I want to relate them in the table of occurrences, but I do not know how

Thanks in advance