Re: Hospital ERD

Designer also uses a notational semantic extension to show mutual exclusion across subtypes in the form of an arc - basically an intersecting line across sub-type relationships to the common generalized entity.

Regards,

Dan Guntermann

"Tony" <andrewst_at_onetel.net.uk> wrote in message news:c0e3f26e.0402040625.75ab57e2_at_posting.google.com...
> "Roy Hann" <rhann_at_globalnet.co.uk> wrote in message
news:<bvqkmu$saq$1_at_sparta.btinternet.com>...
> > "Portroe" <fb_at_oooi.com> wrote in message
> > news:bvqi77$sea$05$1_at_news.t-online.com...
> > > Charge Nurse, Medical Director, personnel officer, Doctor etc of
course
> > > all have differing functions, and differing interactions with the
other
> > > attributes
> > >
> > > the Charge nurse will have hundreds of connected records over a month,
> > > ie. medication ordered, The Medical director significantly less etc
> > >
> > > is there a source for Sample ERDs where I can see how people typically
> > > cope with multiple subclasses 'diagramatically' ?
> >
> > It ain't rocket science.
> >
> > You just put all the common attributes in one table (the super table),
and
> > have 1-to-0-or-1 relationships with one or more subtables that have the
> > distinct attributes. If the subtables in turn can have further
subtables,
> > repeat.
> >
> > Of course the big problem is that none of the graphical conventions were
> > designed by anyone who had much of a clue what they were really doing,
so
> > they can't represent the very important restriction that a table can't
> > simultaneously have two (or more) subtables directly referencing it (if
> > that's what is required). i.e. you can't draw a diagram that shows that
a
> > staff member cannot simultaneously be a phlebotomist and a neurosurgeon,
or
> > salaried and casual.
> >
> > SQL is similarly botched when it comes to imposing suitable constraints.
> > You end up doing "tricks" with keys, which I dislike intensely.
> >
> > Roy Hann
>
> The Richard Barker notation used in Oracle Designer CAN represent the
> fact that entity subtypes cannot overlap. It uses boxes within boxes
> to represent subtyping.
Received on Thu Feb 05 2004 - 03:19:22 CET