# Re: cdt glossary [Graph] (was: what are keys and surrogates?)

From: David Cressey <cressey73_at_verizon.net>
Date: Fri, 11 Jan 2008 12:35:36 GMT
Message-ID: <soJhj.5371\$tZ6.4658_at_trndny03>

"David BL" <davidbl_at_iinet.net.au> wrote in message news:3c251cee-7aab-43e6-8b78-8d7311cb1eb8_at_k39g2000hsf.googlegroups.com...
> On Jan 11, 5:12 pm, mAsterdam <mAster..._at_vrijdag.org> wrote:
> > David BL wrote:
> > > Keith H Duggar wrote:
> > >> David BL wrote:
> > >>> Marshall wrote:
> > >>>> An interesting note, by the way: functions are relations...
> > >>> Isn't it more precise to say that the graph of a function is a
> > >>> relation?
> > >> No, it isn't.
> >
> > >>http://mathworld.wolfram.com/Function.html
> >
> > > From mathworld a relation
> >
> > > http://mathworld.wolfram.com/Relation.html
> >
> > > is defined as a subset of a cartesian product. If a function is a
> > > relation why do they define a graph of a function f as
> >
> > > { (x,f(x)) | x in domain of f },
> >
> > > as described in
> >
> > > http://mathworld.wolfram.com/FunctionGraph.html
> >
> > That is 'graph' meaning 'plot', not 'a collection of vertices and
> > edges'. In cdt it is the latter meaning that is mostly used (when
> > discussing network and hierarchical databases).
>
> Yes, overloading "graph" can cause confusion.

Fortunatly, we have lots of other words. mAsterdam used "plot". My favorite is "chart". A close second is "diagram", although I tend to use "diagram" for a different kind of picture.

The use of "graph" in the cdt sense is too valuable to give up. AFAIK, the cdt sense agrees with the mathematical sense. My inital exposure to this meaning of "graph" comes from Niklaus Wirth in "PASCAL User Manual and Report". Received on Fri Jan 11 2008 - 13:35:36 CET

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