# Re: Is a function a relation?

Date: Wed, 24 Jun 2009 15:15:58 -0400

Message-ID: <OXu0m.1685$j84.941_at_nlpi061.nbdc.sbc.com>

"David BL" <davidbl_at_iinet.net.au> wrote in message
news:a324e279-9814-4d30-a32a-a85396cec7e6_at_a39g2000pre.googlegroups.com...

> On Jun 24, 12:44 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:

*>>
**>> While I would agree that the physical representation of the symbols and
**>> combinations of symbols that compose formal language terms is irrelevant,
**>> if
**>> what is in the Universe of Discourse can exist in time and space, then
**>> database values can exist in time and space. A value is the result of
**>> applying for a given term the valuation function which maps terms
**>> expressed
**>> in a formal language to things in the Universe of Discourse under an
**>> interpretation.
**>
**> I prefer to consider the RM as a pure mathematical formalism divorced
**> from "interpretations" (i.e. external predicates and so forth).
*

I can't see how that is even possible, since the extension of a predicate, regardless of whether it is internal or external, is a collection of atomic formulae, each of which must be judged to be true or false under an interpretation. Under the Closed World Interpretation, only those atomic formulae that are judged to be true are represented, but the judgement must still be made, and that requires the assignment of meaning to each term in each atomic formula. I am not saying that the assignment of meaning and the judgement of truth which are the constituents of interpretation should not be isolated, but I think it is a gross oversimplification to deny that they play a part altogether in relational database theory.

>> How, then, can a pure mathematical system be a

*>> sufficient logical model for things that can change?
**>
**> It is true that a single database value cannot model things that can
**> change (into the future). However database systems are variables not
**> values.
*

Received on Wed Jun 24 2009 - 21:15:58 CEST