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

Date: Sat, 12 Jan 2008 10:48:25 -0800 (PST)

Message-ID: <3f8e5156-c545-4ea4-bb95-a574bdd5d977_at_l32g2000hse.googlegroups.com>

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. I don't really see any problem there - if it's vital to know D and C then they will be stated, and if they are not, well we can still formulate an approximation of them by looking at the elements of the couples in G anyhoo.

Now Multivalued Functions - there's worth something arguing about ;) Received on Sat Jan 12 2008 - 19:48:25 CET