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_at_phobos.telenet-ops.be>
>
> Please clarify whether tour are talking about the RM views and queries or
> about something else.
>
> Cannot we just use the notion of data type (aka domain) instead ?
Date: Sun, 03 Jul 2005 13:15:04 GMT
Message-ID: <sxRxe.136269$3i5.7167004_at_phobos.telenet-ops.be>
VC wrote:
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> news:xxBxe.135773$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