[Uml-user] Entity Relationship Diagrams in 1.4

[Dr Robert Sanderson]

>>> 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)

The main problem with ERDs is that there isn't a single standard way to 
represent them, so my problem is that the textbook for the class I've
taken over to teach is using an ... interesting ... mishmash of common ERD 
elements + UML :/

Perhaps this is available now, but I can't find it, you can also put 
directions on the associations as a solid black arrowhead next to the name 
of the association, rather than an arrowhead on the end of the 
association.
You can do this, for example, in dia and gaphor.

Rob

       ,'/:.          Dr Robert Sanderson (azaroth at liverpool.ac.uk)
     ,'-/::::.        http://www.o-r-g.org/~azaroth/
   ,'--/::(@)::.      Dept. of Computer Science, Room 805
,'---/::::::::::.    University of Liverpool
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