Newbie help with ER diagrams

From: me <toenails777_at_hotmail.com>
Date: Thu, 5 Dec 2002 01:43:18 -0800
Message-ID: <LdEH9.25136$EY.4943_at_fe01>

Hello all. I was wondering if anyone could help me with an ER diagram I'm trying to build, but I don't see how to do it. I can see how to do it in a programming language say C++, but not with ER diagrams.

Suppose I have three entities: A, B, and C. B "is a" A, and C "is a A" also, but B also "has a" C. In programming, I'd have:

class A
{

};

class C: public A
{

};

class B: public A
{

    C myCClass;
};

In an ER diagram, I guess I want to express aggregation. So I have:

---

             |        A       |
             -------------
               |             |
               |             |
          ------      ------
          \ is a /      \ is a /
           \     /        \     /
             \ /            \ /
              |              |
              |              |
         ------      ------
         |   B  |      |   C  |
         ------      ------

How would I express aggregation between B and C?

Thanks.

me Received on Thu Dec 05 2002 - 10:43:18 CET