Re: Database design, Keys and some other things

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.

> 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> }

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> }

Now if one can't reference P through natural keys, or it is inefficient processing-wise to do so, it is acceptable to use some sort of surrogate. However this is also not part of our statement about the world but rather a reference for P, so it should be an attribute in M.

Hope this makes more sense. All best, jog. Received on Wed Sep 28 2005 - 04:06:54 CEST