ER diagram question
Date: 19 Jan 2004 14:48:55 -0800
Message-ID: <28a69e7c.0401191448.5dbfa676_at_posting.google.com>
Hi everybody,
It's been a while since I followed that course in college on database theory and my ER diagram skills are a bit rusty, I was hoping some of you might be willing to help me out.
I'm setting up a database, where, among others, I have the following
entities:
Projects, Customers and Communications
A customer can have multiple projects and a project can have only 1
customer, so there's a 1:N relationship between customers and
projects. This is not the thing that's troubling me, it's the
communications (being a synopsis of any communication between the
company and the customer about the project, can be anything from a
phone call to an email ).
A project can have many communications and a communciation will have
as topic 1 project, so there's a 1:N relationship between projects and
communications. But a customer can also have many communications and a
communication is always originating from one customer, thus there is
also a 1:N relationship between customers and communications, forming
a circle in my ER diagram.
I can remember vaguely that for some reason you don't want to have
circular references in your ER diagram (is this correct? If so, could
someone refresh my memory why this is so?) so my question is, how
would I solve this?
Or should I just let the communications table have a layout something
like:
| communication_id (PK) | project_id (FK) | customer_id (FK) | communication | ?
Thanks for any help, Jonck Received on Mon Jan 19 2004 - 23:48:55 CET