Re: Is a function a relation?

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