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Re: Drawing arcs on ER diagrams

From: Frank van Bortel <frank.van.bortel_at_gmail.com>
Date: 19 Oct 2006 03:36:25 -0700
Message-ID: <1161254184.989193.75350@k70g2000cwa.googlegroups.com>

Liz J schreef:

> "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

Arcs (in Oracle Designer) designate an exclusive OR to a super/subtype entity relationship; aren't the circles simply to identify which relationships are in the arc (as the drawing may become cluttered, and more than one relation (line) may cross the arc)?

If you are using Oracle Designer, the online help should explain this Received on Thu Oct 19 2006 - 05:36:25 CDT

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