# Re: Normalisation

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
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.
>>>>
>>>>
>>>>
>>>>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
Received on Fri Jul 08 2005 - 23:30:05 CEST

Original text of this message