Re: BCNF and relational algebra

From: Perception <perceptionist2000_at_yahoo.com>
Date: Mon, 23 Feb 2004 01:56:31 +0000 (UTC)
Message-ID: <c1bmkf$6r$1@titan.btinternet.com>

"Bob Badour" <bbadour_at_golden.net> wrote in message

news:vr2dnf6SC-bv1aTd4p2dnA_at_golden.net...

> "Perception" <perceptionist2000_at_yahoo.com> wrote in message
> news:c1bcs9$89q$1_at_hercules.btinternet.com...
> > "Bob Badour" <bbadour_at_golden.net> wrote in message
> > news:NY2dnV0uDtJmkKTdRVn-uw_at_golden.net...
> > > What do you suppose the unary relation of dates means?
> > >
> > >
> >
> > Thanks for the reply.
> >
> > To answer your question: the unary relation means that every date is
> > associated with more than one value for every other attribute (that is,
> Date
> > only determines itself).

>

> That tells me what Date determines, but it does not tell me what it means.
> Is every date for all time in the unary relation? What does it mean for a
> specific date if it is in the relation? What does it mean for a specific
> date if it is not in the relation?

>

Sorry for the misunderstanding. Specific dates correspond to when a patient visited a doctor. Thus if a date is in the relation, it means a patient had seen a doctor/attended a clinic on that date.

The original un-normalised datebase had tuples of the form:

Patient Id, Patient Name, Ward, Date, Clinic, Doctor

with data of the form, for instance

3842, Smith, 2, 6.7.03, 4, Anderson

                         9.9.03, 3, Haswell

corresponding to the above attributes for one particular patient. Received on Sun Feb 22 2004 - 19:56:31 CST