Re: Ternary Relationship cardinality

From: <miklesw_at_gmail.com>
Date: 19 Sep 2006 05:00:00 -0700
Message-ID: <1158667199.894104.277050_at_d34g2000cwd.googlegroups.com>


> It depends a bit on which ER dialect you happen to be using. Strictly
> speaking, if you specify that A IS-A C and B IS-A C this only means
> that every A is a C, and every B is a C. So it does not mean that A and
> B are disjoint (i.e., there can be entities in both A and B) or that
> every C is either an A or a B. Usually there are special combined
> isa-edges to denote the latter two constraints. But, again, this may
> depend on the dialect your instructor / professor is using, so be sure
> to check the IS-A semantics in the notation you have to use.

Thanks for the tip.. According to this presentation I got from the net, IS-A's can be partial or total (in my case they're partial).. will add a note in the ER stating all entities in hierarchy are Concrete classes just in case..

Mike Received on Tue Sep 19 2006 - 14:00:00 CEST

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