Re: Weak Entity

I think the reason why theres an emphasis on having a 1-N relationship with another strong entity is so that you can treat that relationship as a supporting relationship and the strong entity can lend its keys to form keys of the weak entity relation.

"Jan.Hidders" <hidders_at_hcoss.uia.ac.be> wrote in message news:3da9d555$1_at_news.uia.ac.be...
> In article <aoc55a$kdv$1_at_news.ctimail.com>,
> Peter Kwok\\ <peterkwok628_at_yahoo.com> wrote:
> >In ER diagram, should weak entity be related to strong entity in 1-N
> >relationship?
> >i.e.
> >Correct:
> >Strong Entity----------(1)-Relate-(N)----------Weak Entity
> >
> >Wrong:
> >Strong Entity----------(M)-Relate-(N)----------Weak Entity
>
> No.
>
> For example:
>
> Element --(M)-Is_contained_in-(N)-- Non-empty_Set
>
> Clearly non-empty sets cannot exist without their elements and they have
no
> attributes to form a key.
>
> However, some definitions of the ER model do have this restriction, so it
> also depends a bit on what book you are using and how smart your
instructor
> is. :-)
>
> -- Jan Hidders
>
>
Received on Mon Oct 14 2002 - 01:17:12 CEST