Re: ER Diagramming Question

On Mar 26, 3:17 pm, "Vince" <vinn..._at_yahoo.com> wrote:
> On Mar 26, 11:27 am, "Michael P." <mich..._at_michaeljpatterson.com>
> wrote:
>
> > This may not be the most appropriate group to post this question, but
> > any number of the users will probably have the answer.
>
> > When reading an ER diagram using Crow's feet notation, it's my
> > understanding that a single has mark means that end of the
> > relationship is mandatory. Does a double has mark mean anythign
> > different or is that how the ERD tool represents that relationship?
>
> > Also does the optional symbol on top of a has have any extra meaning.
> > I've run into this on the many side of the relationship?
>
> Michael,
> The single indicates one and the crow's feet indicates many.
>
> Optionality would be indicated by solid (must) and dashed (may have)
> notation.
>
> The classic dept-to-emp relationship, there would be a single, dashed
> line on the dept end and crow's feet, solid line on the emp end,
> indicating a dept may have one or more emps and an emp can must have
> only one dept. (This model is a little dated. Afterall, what emp stays
> in only one dept for the duration of their tenure, but I digress...)
>
> The above is true for Oracle's Designer ERD modeling tool. Not sure
> what other products use.
>
> Vince

This link to James Martin of Information Engineering notation (crows feet) and other notations
has explantions of each style etc.

[url]http://www.aisintl.com/case/method.html[/url] Received on Wed Mar 28 2007 - 12:58:38 CDT