Re: How to add relationship lines?

[Steve Litt <slitt troubleshooters com>]

On Mon, 6 May 2013 23:49:00 +0300
Genadi Saltikov <carmageddon gmail com> wrote:

> Hello Steve!
> Apologies for not sharing what I found, I thought everyone on the list
> knows :)
> Basically, after dissecting the original .DIA file Hans linked me to,
> I figured out that the relationships like 1:1, 1:N etc, were defined
> as properties of the RELATIONSHIP objects!

I'd never used Dia's ER tools, so thanks for filling me in. After
viewing Hans's diagram, I understand what you mean. Keep in mind I
never took the course you're taking -- to me all I was drawing were
flowcharts, hierarchy charts and block diagrams. :-)

> In my opinion, this is far from trivial, especially that it is not
> explained in the documentation.
>
> What I meant about cardinality, I have drawn in red color in the
> following picture, so you can see it without misunderstanding what I
> mean.
> https://www.dropbox.com/s/9asujpcd6o50nve/2013-05-06%2023.43.38.png
> Please note how this relationship relates to 3 entities - currently
> in Dia, I have not found a way to set more than 2.

Now I understand. I'm wondering whether the ternary relationship
described on that page of your book (and thanks for that -- it
explained everything, including things I never knew before), really
does justice to the true relationship between departments, locations
and employees. I see it's a shorthand, but any two can relate totally
without the third. When I've coded database apps from database tables,
my recollection is I had a single relationship for exactly two tables,
and then more relationships for other tables. See this diagram:

http://www.a3b3.com/stuff/tri_relationship.dia

If I had to write code based on the diagram, I'd find the explicit
relationships more explicit. But then again, I've never been trained in
what you're doing. Until now, that is, and thank you for that.

Thank you for teaching me this brand new capability of Dia. I've used
Dia over ten years, and never knew this existed.

Anyway, please let me know what you think about the explicit
tri-relationship.

Thanks,

SteveT

Steve Litt                *  http://www.troubleshooters.com/
Troubleshooting Training  *  Human Performance