Re: Recursive (Unary) Relatinoships

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.

Kind regards,

    Jan Hidders Received on Sun Nov 12 2000 - 21:47:49 CET