Re: Normalisation
Date: Fri, 08 Jul 2005 21:30:05 GMT
Message-ID: <xfCze.140548$uH4.7139418_at_phobos.telenet-ops.be>
Jon Heggland wrote:
> In article <03fze.139573$4A5.7335025_at_phobos.telenet-ops.be>,
> jan.hidders_at_REMOVETHIS.pandora.be says...
>
>>>>These sets are very similar to unary relations. Treating them >>>>differently would make not much sense because there are simple >>>>operations that transform one into the other. >>>> >>>> >>>>>Why not about strings? >>>> >>>>They are not very similar to relations. :-) >>> >>>A set can be transformed into a unary relation with a simple operation. >>>A string can be transformed into a binary relation (integer and >>>character) with a simple operation. >> >>That requires logarithmic space, and not constant space as my >>transformation. So it is arguably more complex.
>
> Please elaborate. Assuming for the sake of the argument that you are
> right, so what?
It indicates that in one case there is a larger similarity than in the other because you meed more work to do the transformation. You're not asking me to explain the stated complexity classes of the operations, are you?
>>>>Besides, most nested >>>>relational algebras I know are not equipped with an operation for >>>>unnesting strings. >>> >>>That's just because it's a pretty useless thing to do. :) My point it >>>that the difference between sets and strings in this context is pragma, >>>not logic. >> >>My definition of 1NF doesn't make that distinction.
>
> Your definition of 1NF seems singularly useless if you cannot use it to
> determine the quality of a relvar in any way---unless you introduce a
> lot of unstated and pragmatic assumptions.
> It is also rather
> complicated, imo, since you have to refer to operations over signatures
> and proper classes as opposed to sets/domains.
The definition does not refer to proper classes, and it is always a bit dangerous to call something complicated just because you had trouble understanding it. :-) As any good database researcher you probably know and understand the notion of "genericity". Just as a test to see if you really understood it, can you tell me the relationship between this notion and the notion of 1NF I defined?
> I see your point, but for me it smacks of the kind of reasoning that
> leads you to "denormalise" relations because join is too complex and
> slow. It may be the right choice at the implementation level, but we
> should separate that from the logical level.
- Jan Hidders