BCNF and relational algebra

I have the following relations (expressed as functional dependencies) which I consider to be in BCNF (please correct me if I'm wrong):

Patient Identifier -> Patient Name, Ward Date
Doctor -> Clinic

Now the problem here is that I am unable to deduce how to make any real query on these set of data because there are no common attributes between the relations. Is it even possible for relations under BCNF to have no common attributes? Note that the original relation was identical expect it had the additional functional dependency: Patient Identifier, Date, Doctor -> Patient Name, Ward, Clinic (i.e. the attributes on the LHS were the primary key). I decomposed the relation as I have shown above given that I knew each Patient Identifier was unique, a patient would never change wards but could attend several clinics, on each occasion a patient would see one doctor, doctor names were unique and that doctors were only associated with a single clinic. Now I believe that I have made a reasonable interpretation of this information both in my choice of primary key in the original relation (i.e. Patient Identifier, Date and Doctor) and in my decompositions into BCNF (every determinant is a candidate key).

Thus, if I wanted to list, say, all patient identifiers and names for all patients attending a certain clinic and having not been seen by a certain doctor how on earth would this be possible in relational algebra given that I cannot join over any common attribute?? So either I have made a mistake in my decomposition or there are some techniques that I am not aware of (that can link the FDs in some way).

In either case I would appreciate any help or clarification!

Thanks in anticipation. Received on Sun Feb 22 2004 - 21:00:52 CET