Re: Normalisation

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Wed, 06 Jul 2005 18:38:24 GMT
Message-ID: <AyVye.138732$g63.7370802@phobos.telenet-ops.be>

Jon Heggland wrote:
> In article <PwBye.138032$Nn7.7012386_at_phobos.telenet-ops.be>,
> jan.hidders_at_REMOVETHIS.pandora.be says...
>

>>>Does it matter whether my unnest_string is system defined (by the DBMS) 
>>>or user-defined?
>>
>>Yes.  

>
> Are you serious? If unnest_string is system defined, relations with
> string attributes are in 1NF, but if the exact same operator is user
> defined, they are not? Why on earth would you want to make such a
> distinction?

Hmm. You're right. I have to apologize here because I don't know why I said that. The definition I gave doesn't even mention that distinction.

>>Note btw. that if user-defined functions are restricted to the 
>>domains (their input and output types are only domains) then you cannot 
>>define such an operation as a user-defined function.

>
> Let me try to define such an operator.
>
> unnest_string takes a relation IN and an attribute name A as arguments,
> returns a relation OUT. The type of attribute A in IN is character
> string.

Ah, but now you are using the domain or relations, right? There is a problem with that domain. It doesn't exist. The collection of all relations is a proper class, and not a set, but domains have to be sets.

• Jan Hidders

Received on Wed Jul 06 2005 - 13:38:24 CDT