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: Sun, 03 Jul 2005 13:15:04 GMT
Message-ID: <sxRxe.136269$3i5.7167004@phobos.telenet-ops.be>

VC wrote:
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> news:xxBxe.135773$vq.7300203_at_phobos.telenet-ops.be...
>

>>VC wrote:
>>
>>>"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message 
>>>news:eHrxe.135259$JD6.7251058_at_phobos.telenet-ops.be...
>>>
>>>
>>>>vc wrote:
>>>>
>>Anyway, why do you want specifically an algebra? You don't need one for 
>>asking queries, not for defining views and you don't need one for query 
>>optimization, so why bother?

>
> Please clarify whether tour are talking about the RM views and queries or
> about something else.

All of them, really. FDM-like models, OODB data models, and also the RM.

> Well, apparently, I am not as smart as most of your students are. Please
> provide a definition of "conceptual object type".

A unary predicate.

>>>OK.  Firstly,  why do we care about 'value representation'  at all ?
>>
>>Because otherwise we couldn't indicate in an ORM schema that the name of a 
>>department is represented as a string.

>
> Cannot we just use the notion of data type (aka domain) instead ?

We can, with the additional restriction that the elements of the domains must have some kind of lexical representation.

Jan Hidders

Received on Sun Jul 03 2005 - 08:15:04 CDT