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

Date: Sun, 13 Jan 2008 13:57:31 -0800 (PST)

Message-ID: <5e3b9fd8-9299-47cb-8c36-620b4c20501c_at_v4g2000hsf.googlegroups.com>

On Jan 13, 8:04 pm, David BL <davi..._at_iinet.net.au> wrote:

> On Jan 13, 3:48 am, JOG <j..._at_cs.nott.ac.uk> wrote:

*>
**>
**>
**> > On Jan 12, 8:14 am, David BL <davi..._at_iinet.net.au> wrote:
**>
**> > > On Jan 12, 2:24 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
**>
**> > > > On Jan 12, 1:05 am, David BL <davi..._at_iinet.net.au> wrote:
**> > > > > Really! I have seen a (mathematical) relation formally defined as a
**> > > > > subset of a cartesian product (and not an ordered tuple) on many
**> > > > > occasions.
**>
**> > > > Bit confused by this - a cartesian product generates a set of ordered
**> > > > tuples (over which a function is a subset), and all the hyperlinks you
**> > > > listed seemed to follow that description.
**>
**> > > Do you agree that most authors define a binary relation as a set of
**> > > ordered pairs? In an earlier post you said a function is the ordered
**> > > triple (D,C,G). How do you reconcile saying that a function is a
**> > > (binary) relation?
**>
**> > Relations are formally described by the ordered triple (D,C,G), but
**> > are often informally described by just G.
**>
**> So all those authors that define a binary relation as a set of ordered
**> pairs are being informal? I don't agree with that.
**>
**> Check out the section under formal definitions in
**>
**> http://en.wikipedia.org/wiki/Relation_%28mathematics%29
**>
**> Are you saying that definition 1 is informal?
*

I don't see why you'd think so - in the article, first the domains, x1...xn, are stated. Then the graph is specified as a subset of the cartesian product of x1..xn. Seems relatively formal to me - domains and a graph (albeit for an n-ary as opposed to a binary relation). Received on Sun Jan 13 2008 - 22:57:31 CET