Re: Codd's Information Principle
Date: Mon, 02 Nov 2009 01:27:39 GMT
Message-ID: <fAqHm.51166$PH1.30497_at_edtnps82>
Bob Badour wrote:
...
> I suspect you simply do not include enough context to decipher what you
> are saying. If I have a relation variable, R, at any given time, its
> extension is simply its value. Is it not? Since R can have different
> values at different times, it can have more than one extension; albeit,
> only one at a time.
Thanks, I'll ponder that. The only comments I want to make right now are i) that I prefer to avoid talking about relvars until some choice of language is made, which choice seems premature, eg., I can imagine an environment where the programmer's context doesn't include assignment, and ii) I think expressions have a value and extensions have a value (maybe you are more pertinent saying that they are values, not sure) and those two values are equivalent in Codd's RM context - my attitude about equality as far as machines are concerned is that it should be determined only by typical machine-level comparison instructions which I hope keeps various language notions of equality out of the picture as far as interpreting values is concerned. This is perhaps narrower or stricter than most people want, maybe it's an unnecessary distinction too but I'd rather be careful about it. Received on Sun Nov 01 2009 - 19:27:39 CST