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

Date: Sun, 13 Jan 2008 12:04:31 -0800 (PST)

Message-ID: <b64c74e3-ff49-4873-97ec-f345b52a95e0_at_d21g2000prf.googlegroups.com>

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? Received on Sun Jan 13 2008 - 21:04:31 CET