Re: Recursive (Unary) Relatinoships
Date: Tue, 14 Nov 2000 11:29:09 +0200
Message-ID: <3A1105E5.3FDE71F8_at_otenet.gr>
Jan Hidders wrote:
> gkiourtas michail wrote:
> > -=-=-=-=-=-
> > Jan Hidders wrote:
> >
> > > gkiourtas michail wrote:
> > > > Can someone present the following meanings in an easy to understand way?
> > > >
> > > > What is the usefullness of these meanings in database design?
> > > > a) Symmetric Recursive Relationship
> > >
> > > A binary relationship is recursive if it holds between entities of
> > > the same class. E.g. the friend-of relationship holds between two
> > > persons. Such a relation is symmetric if it holds that the
> > > relationship holds between p1 and p2 then it also holds between p2
> > > and p1. In this example this would mean that if p1 is a fried of p2
> > > then p2 is also a friend of p1. The usefulness of this concept is
> > > that it defines a database constraint that should be guarded by the
> > > database.Further information for this sentence?
>
> The way you insert your text into mine is a bit confusing. You should
> type your own text below the text that you quote and leave an empty
> line in between. That way it is easier to see what you wrote and what
> the person you quote wrote.
>
> And by now I would like to know why you want to know all these things,
> because I am getting the feeling that I am doing somebody's homework.
> Not that I wouldn't want to help you with that but I would make sure
> that you had to think things through instead of just writing them down.
> You will not learn anything from just copying my answers.
I try to "fill the holes" in the theory.You can answer by referring to textbooks.But I don't think my questions are
covered in these,for example my postings about look-across cardinalities,possibility relationships etc
Best Regards, Mike
> >
> Kind regards,
>
> Jan Hidders
Received on Tue Nov 14 2000 - 10:29:09 CET