David Cressey wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:474dd64a$0$5285$9a566e8b_at_news.aliant.net...
>
>>rpost wrote:
>>
>>>paul c wrote:
>>>
>>>[...]
>>>
>>>>Regarding ER, here are some quotes from Codd's book (available for free
>>>>at acm.org). The sarcasm of the second one made me laugh.
>>>
>>>The criticisms you quote may be amusing, and they have merit, but
>>>they ultimately miss the point. The distinction between entities and
>>>relationships: entities have identity (they can be referred to;
>
> attributes
>
>>>can have entity-valued domains), while relationships do not (they are
>>>completely identified by their, possibly entity-valued, attributes).
>>
>>Except that relationships have identities too. The identity of the
>>relationship between an employer and an employee, for example, is a
>>contract. The relationship between a mother and a child, for example, is
>>the event of birth. etc.
>>
>>>[...]
>>>
>>>
>>>>3. Even if this distinction had been precisely defined, it would have
>
> added
>
>>>>complexity without adding power. Whatever is conceived as entities, and
>>>>whatever is conceived as relationships, are perceived and operated
>>>>upon in the relational model in just one common way: as relations.
>>>
>>>This is the exact problem Chen identified. In the relational model
>>>it is impossible to have entity-valued attributes, which, in practice,
>>>we have a huge amount of.
>>
>>Entities are figments of our imaginations.
>
> You are an entity.
Am I? Or am I billions of cellular entities? Or am I part of a larger
community entity?
Received on Thu Nov 29 2007 - 07:18:59 CST
