Date: Wed, 31 Oct 2007 18:44:54 -0300
>>paul c wrote: >> >>>David BL wrote: >> >>>>On Oct 31, 4:31 pm, "Roy Hann" <specia..._at_processed.almost.meat> >> >>>... >> >>>>>1NF does not *require* that values be atomic. It asserts that values >>>>>will >>>>>be *treated as* atomic. Big difference. Essential difference. >> >>>>>Roy >> >>>>Can that be formalised? I agree with Bob that in general we have a >>>>set of operators and they can allow us to see internal structure. >>>>What does it mean for a value to be *treated* as atomic? >> >>>I think it means that relational algebra operators are not allowed to >>>decompose it. >> >>Actually, the structure is illusory and representation-dependent. >>Domains have operations that appear to reveal internal structure even >>when that internal structure may not physically exist.
> One hundred and twenty three is an atomic value; a natural
> number. The idea that there is a 1, a 2, and a 3 in there is illusory.
> (Or rather, it is an artifact of the representation, not an
> artifact of the value.)
> You can write an expression that will give you those things,
> but that shouldn't lead us to any conclusions.
> X / 10 % 10 will give us the tens place. But what then
> are we to make of X / 9 % 9? It gives us the nines place
> in a base 9 number.
It's ironic you should mention base 9. It's a little-known fact that, if a number is evenly divisible by 8, the sum of the digits of the number in base 9 is also evenly divisible by 8. And if one repeats the process with that sum until the resulting sum has only one digit and if the original number was divisible by 8, the one remaining digit will be 8.
It's like magic. So it's really ironic you should mention base 9 in particular. Received on Wed Oct 31 2007 - 22:44:54 CET