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 19:02:53 GMT
Message-ID: <xxBxe.135773$vq.7300203@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:
>>
>>>What's the (a) formalism for the FDM comparable to the RM  (the FDM
>>>structure/the FDM algebra/FDM constraint definitions).  Daplex does not
>>>quite cut it as an 'algebra'.
>>
>>Why not? Because it has operations with side effects?

>
> An algebra is a set S together with operations on S.

Then why did you put it between quotes? 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?

>>>I tried to read one of the articles you've referenced
>>>(http://www.orm.net/pdf/ER96.pdf, "Conceptual query language"),  but
>>>quickly stumbled over the words "semantic" and "conceptual".
>>
>>:-) Yeah, ORM people like to use those words a lot. I wouldn't worry too 
>>much about it. You can understand the query language w/o understanding 
>>what those words exactly mean.

>
> Can your response be interpeted as meaning that the article is essentially
> non-sensical (we do not care what the words the authors use mean) ?

No, just that the specific meaning of those words is not essential for understanding the query language and that, since you seem an intelligent person you will probably pick up their meaning as we go along. Most of my students seem to manage it, so I don't see why you couldn't.

>>>What does NOLOT being 'abstract' mean ?
>>
>>That there is no value representation associated with non-lexical objects.

>
> 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.

Jan Hidders

Received on Sat Jul 02 2005 - 14:02:53 CDT