Re: ER diagram question

jonck_at_vanderkogel.net (Jonck van der Kogel) wrote:
>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
Can a Customer have a Communication independent of a Project? Received on Tue Jan 20 2004 - 05:18:08 CET