Re: One-To-One Relationships

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 02 Dec 2007 11:47:38 -0400
Message-ID: <4752d39e$0$5266$9a566e8b@news.aliant.net>

David Cressey wrote:

> "Cimode" <cimode_at_hotmail.com> wrote in message
> news:36f20483-5085-4d52-b33d-1ddd85bd6735_at_w56g2000hsf.googlegroups.com...
>

>>On 30 nov, 19:33, JOG <j..._at_cs.nott.ac.uk> wrote:
>>
>>>On Nov 30, 6:03 pm, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:
>>>
>>>
>>>>On Nov 30, 8:19 am, Jan Hidders <hidd..._at_gmail.com> wrote:
>>>>The distinction between entities /
>>>
>>>>>relationships, domain objects / predicates is pretty

>
> well-established
>

>>>>>in linguistics, philosophy and logic.
>>>
>>>>That certainly means you can define them formally in database terms,
>>>>right?
>>>>Here is one such

>
> attempt:http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.2083v1.pdf
>

>>>>It defines an entity as a relation (aka table:-) with a single
>>>>noncomposite key, and relationship as a table with composite key. Does
>>>>this definition pretty much exhausts the entity-relationship theory?
>>>
>>>I like the insight that both 'entities' and 'relationships' are
>>>subtypes of a parent concept, that is simply a set of attributes and
>>>values. I'd like to see a formalization of that which doesn't rely on
>>>relational theory and the concept of keys however, even though I
>>>imagine there would be a direct correspondence.
>>
>>OK I will play devil's advocate and try to believe that entities could
>>be an alternative expression of entities...
>>
>>Quite frankly, I understand the intent but not the need to
>>differentiate relations and entities...
>>
>>I believe somehow that because Relations rely on set theory and
>>relational algebra, it simply has a longer mathematical history and de
>>facto more abstract tools concepts to work with than Entities that
>>seem recent.  I do believe that the keys was simply Codd's way to
>>express *identifiablity* in a way that his IBM audience could be
>>receptive to the rest of the model...I do not perceive keys as a
>>sufficient reason to require differentiation between the two models...

>
> Entities are not recent. Entities are as old as Aristotle. Aristotle was
> not attempting to design databases. Codd was not attempting to reformulate
> the metaphysics of how we understand reality.
>
> Chen's contribution was to provide a model in which the information
> requirements can be stated without presupposing a design that is going to
> meet those requirments.

In exactly what ways did Chen's contribution improve over the previously existing conceptual analysis techniques? Received on Sun Dec 02 2007 - 09:47:38 CST