# Re: Is a function a relation?

Date: Tue, 30 Jun 2009 02:15:32 GMT

Message-ID: <op.uwbe76koq7k8pw_at_imac.local>

On Sat, 27 Jun 2009 12:55:16 +1000, David BL <davidbl_at_iinet.net.au> wrote:

> On Jun 27, 10:10 am, "Joe Thurbon" <use..._at_thurbon.com> wrote:

[...]

*>>
*

>> What are you talking about when you say interpretation?

*>
**> I completely agree that an interpretation in model theory is a
**> mathematical construct. I don't believe Brian was using the word
**> interpretation in that sense, because he spoke about a UoD that can
**> exist in time and space. His words:
**>
**> "... 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 assumed he was talking about the idea to interpret mathematical
**> relations as predicates that apply to the real world. i.e. external
**> predicates.
**>
*

Sorry about the delay in replying, this conversation seems to have moved on. But thanks for clarifying.

> As C.Date says:

*>
**> "... while internal predicates are a formal
**> construct, external predicates are an informal
**> construct merely. Internal predicates are (loosely)
**> what the data means to the DBMS; external
**> predicates, by contrast, are what the data means
**> to the user."
**>
**> An external predicate, being informal, is typically stated in natural
**> language.
**>
*

Out of interest, Date also states his formal predicates in natural language, at least in Logic and Databases.

Cheers,

Joe
Received on Tue Jun 30 2009 - 04:15:32 CEST