Re: One-To-One Relationships

From: Bob Badour <>
Date: Sun, 02 Dec 2007 11:47:38 -0400
Message-ID: <4752d39e$0$5266$>

David Cressey wrote:

> "Cimode" <> wrote in message

>>On 30 nov, 19:33, JOG <> wrote:
>>>On Nov 30, 6:03 pm, Tegiri Nenashi <> wrote:
>>>>On Nov 30, 8:19 am, Jan Hidders <> 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,
>>>>Here is one such

> attempt:
>>>>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 - 16:47:38 CET

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