Ternary Relationship cardinality
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Newsgroups: comp.databases.theory
From: mikl...@gmail.com
Date: 19 Sep 2006 05:00:00 -0700
Subject: Re: Ternary Relationship cardinality
> It depends a bit on which ER dialect you happen to be using. Strictly Thanks for the tip.. According to this presentation I got from the net, > 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. 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 You must Sign in before you can post messages.
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