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 17:53:38 GMT
Message-ID: <CwAxe.135730$_81.6969472@phobos.telenet-ops.be>

VC wrote:

> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message 
> news:NYqxe.135226$KN7.7252062_at_phobos.telenet-ops.be...

>>VC wrote:
>>
>>>Hi,
>>>
>>>[...]
>>>"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
>>>news:IVhxe.135039$l56.6861917_at_phobos.telenet-ops.be...
>>>>
>>>>Data values are special objects that have one or more representations
>>>>associated with them by which they are identified.
>>>
>>>What's that supposed to mean ? 'Value' is just an element of a domain
>>>(data type), like, say, '1' is_a_member_of Integer. Are you proposing
>>>a new definition of 'value' ?
>>
>>Not really, I'm restricting it slightly. I'm using the one that says that
>>a value is something that (1) has one or more representations, i.e., can
>>be encoded in memory and (2) is identified by that encoding in the sense
>>that some equivalence relation over all possible representations is
>>defined and each value corresponds to an equivalence class defined by it.

> 
> (1) implies that you are concerned with implementation (the way the value is 
> encoded in memory).

No, what we are concerned with is the property that it is something that I can denote. That has nothing to do with implementation.

>>>[It's not idle curiosity on my part (as was with the 'return' word). I
>>>am genuinely interested what the current formalism for the
>>>object/network/xml data model is.]
>>
>>XML doesn't belong in that row, it is an entirely different beast.

> 
> How is it different ? Is it not just a notation for trees (with a lot of 
> other baggage admittedly) ?

Yes, ordered, node-labeled trees, whereas the other two are more about graphs.

• Jan Hidders

Received on Sat Jul 02 2005 - 12:53:38 CDT