Re: Entity Relationship Diagrams in 1.4

On Fri, Jan 07, 2005 at 11:13:40AM +0000, Dr Robert Sanderson wrote:
> >>>You can use a class diagram instead.
> >Well, you should use a class diagram really. The ERD is just a subset of 
> >Class Diagram with a different "graphic" representation, isn't it?
> 
> Almost.  But most importantly for my purposes -is- the different graphic 
> representation.
> 
> In an ERD you can have a trinary+ relation as a different type to an 
> entity, normally represented as a diamond.
> 
> So, if you'll excuse the ascii:
> 
> [A] --<>-- [C]
>       |
>      [B]
> 
> To represent the relations in the form of A x B y C
> 
> Rob talksAbout ERD on MailingList
> 
> Then attributes of the relation are often represented as circles or with a 
> dashed line connecting to either the diamond in a trinary or the 
> association line itself if there isn't a diamond.  Which you can't do in a 
> class diagram.
> 
> You can represent the relationship as an Entity in its own right of 
> course, which is what I do at the moment. (Which is much cleaner, IMO)

There seem to be two types of entity relationship diagrams, one where
fieldnames are ovals sprouting off the entities and relationships and
diamonds, and the cleaner ones with entities and lines between them
with crows' feet.

The first two results searching images.yahoo.com shows the difference

http://www.metacase.com/images/er_diagram.gif
http://cispom.boisestate.edu/cis310emaxson/13-23.jpg

Since the second way seemed cleaner, is used by real database
applications such as Krita or MS Access and I could see no advantage
in the more complex way I just did it the second way.  See screenshot
at http://uml.sf.net

>       ,'/:.          Dr Robert Sanderson ([email protected])

Liverpool eh, say hi to Chris Howells.

Jonathan Riddell


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