Re: Optionality on E-R Diagrams

Ryan Shelswell (ryan@nospam.socs.uts.edu.au)
Mon, 27 Mar 1995 16:12:33 +1000 (EST)

On Sun, 26 Mar 1995 pmeric@nospam.vnet.IBM.COM wrote:

> A quick question on the placement of the "optionality circle" on E-R
> diagrams...
>
> Entity A may be related to Entity B, so the optionality circle is placed
> in between the end of the line and Entity A, isn't it?

Goldarnit boy, you bin messin` wit dem IE+ CASE Tools or sumpin'?

... there are many standards, but I like the one you outlined best. It
can be thought of naturally as "A's participation in the relation is
optional".

As for "opposite to cardinality", I read those as "1 A to many B" ==

A o---*--- B
1 M

But-watch-out, because there are some differing standards. Ask Paul
Bennett for analysis if you can't understand an ER, he's good at it.

Ryan