Re: Database design, Keys and some other things

JOG wrote:
> vc wrote:
> >'The sky is blue in the daytime' ain't no predicate. It's an [ambiguous]
> > proposition which could be false or true if it were not ambiguous.
>
> Ok. There exists a meteorlogical observation where [the sky is blue in
> the daytime]. That is the sentence (not a very good one i'll agree, but
> a propositional sentence nonetheless), with the predicate in square
> brackets.

Still not good enough. In logic, a predicate is a statement whose truth depends on the variable(s)ranging over some domains(s). E.g 'x is_older_than y' is a predicate, but 'John is older than Jim' is a proposition. You need to restructure your sentence some more in order to make a predicate out of it.

>
> > It may be useful to know that the predicate's interpretation is not just any
> > set, but a mathematical relation. What relation are talking about ?
>
> Totally right about the sloppy representation i used however. Let me
> rectify that for the "meteorological_observations" table - in terms of
> the finite partial maps that represent the rows of table, correctly
> written the corresponding relation to define it extensionally:
>
>
> P = { <feature: sky>, <colour: blue>, <period: daytime> }

As I said above, this row/tuple is not a predicate, it's a proposition.

>
>
> The extra information I specified in the previous post however, is
> absolutely not part of this statement about the world. Rather it is
> metadata about P:
>
>
> M = { <creator: James>, <created: 1127871055>, <statement: P> }
>

OK. All the talk about predicates aside, why the piece of information above should be treated in a special way and called by the nebulous word 'metadata' ? What is gained by this in comparison to treating the additional attributes as part of the original entity (or being a separate entity) ?

> Hope this makes more sense. All best, jog.
Received on Wed Sep 28 2005 - 16:34:37 CEST