Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Sat, 02 Jul 2005 18:19:13 GMT
Message-ID: <BUAxe.135753$ms1.7223342@phobos.telenet-ops.be>

Jon Heggland wrote:
> In article <IVhxe.135039$l56.6861917_at_phobos.telenet-ops.be>,
> jan.hidders_at_REMOVETHIS.pandora.be says...
>

>>It's the difference between informally stating that certain 
>>fields are surrogate keys and waving your hands a bit, and coming up 
>>with a precise formal theory of what that exactly means.

>
> I don't see where hand-waving and informality enters into it.

In the part where you forget to explain what "surrogate" exactly means.

>>So where do you get the feeling hat this worldview would be 
>>somehow restrictive?

>
> For one thing, I don't like being forced to decide whether something is
> an entity or a relationship.

In FDM-like models you don't have to do that.

>>Data values are special objects that have one or more representations 
>>associated with them by which they are identified. Like LOTs and NOLOTs 
>>in NIAM.

>
> Are you talking about LOTs or NOLOTs now? NOLOTS have reference schemes
> where (the representation of) a value identifies them.

Yes, they can, but that is neither here nor there. Lexical objects are identical to their representation, non-lexical objects are not equal the combination of lexical objects they are identified by. If you are identified by the string "Jon Heggland" then that is not the same as saying that you are identical to that string.

Jan Hidders

Received on Sat Jul 02 2005 - 13:19:13 CDT