Re: Drawing arcs on ER diagrams

"Brian Peasland" <dba_at_nospam.peasland.net> wrote in message news:J7C6Ar.Ior_at_igsrsparc2.er.usgs.gov...
> Liz J wrote:
>> Hi
>>
>> I am learning about arcs on a ER diagram. Please could someone explain
>> the significance of the circles that are on some of the arcs but not
>> others?
>>
>> thanks
>>
>> Liz
>
> There are no standards when it comes to ER diagrams. As such, the textbook
> or software you are using should explain this in more detail.
>
> I some ER diagrams I have seen, the circles denote a connector from one
> page to another. The number in the circle would represent the page number
> where the ER diagram is continued. In other ER diagrams, the circles have
> denoted the "cardinality" of the relation, that is if the relation is
> 1-to-1, 1-to-many, or many-to-many. Finally, I have seen circles to denote
> the attribute names of an entity.
>
>
> HTH,
> Brian
>
>

Thanks for the help. The book (or online course in this case) introduces Arcs and the circles are just there. I think they are probably optionality, but this is really already there in the dotted line.

Liz Received on Wed Oct 18 2006 - 18:24:54 CDT