Re: One-To-One Relationships

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 02 Dec 2007 15:00:27 -0400
Message-ID: <475300d0$0$5296$9a566e8b_at_news.aliant.net>

David Cressey wrote:

> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:4752d39e$0$5266$9a566e8b_at_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?
>
> What are the previously existing conceptual analysis techniques?

Damn! Chen pre-dates all the good ones. Don't you just hate when that happens? Received on Sun Dec 02 2007 - 20:00:27 CET