On Mon, 6 May 2013 23:49:00 +0300 Genadi Saltikov <carmaged...@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 _______________________________________________ dia-list mailing list dia-list@gnome.org https://mail.gnome.org/mailman/listinfo/dia-list FAQ at http://live.gnome.org/Dia/Faq Main page at http://live.gnome.org/Dia
