Re: Weak Entity

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