Re: One-To-One Relationships
From: Brian Selzer <brian_at_selzer-software.com>
Date: Fri, 30 Nov 2007 16:24:07 GMT
Message-ID: <HOW3j.48583$eY.13591_at_newssvr13.news.prodigy.net>
>> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>> news:474dd64a$0$5285$9a566e8b_at_news.aliant.net...
>>
>>>rpost wrote:
>>>
>>>>paul c wrote:
>>>>
>>>>[...]
>>>>
>>>>>Regarding ER, here are some quotes from Codd's book (available for free
>>>>>at acm.org). The sarcasm of the second one made me laugh.
>>>>
>>>>The criticisms you quote may be amusing, and they have merit, but
>>>>they ultimately miss the point. The distinction between entities and
>>>>relationships: entities have identity (they can be referred to;
>>
>> attributes
>>
>>>>can have entity-valued domains), while relationships do not (they are
>>>>completely identified by their, possibly entity-valued, attributes).
>>>
>>>Except that relationships have identities too. The identity of the
>>>relationship between an employer and an employee, for example, is a
>>>contract. The relationship between a mother and a child, for example, is
>>>the event of birth. etc.
>>>
>>>>[...]
>>>>
>>>>
>>>>>3. Even if this distinction had been precisely defined, it would have
>>
>> added
>>
>>>>>complexity without adding power. Whatever is conceived as entities,
>>>>>and
>>>>>whatever is conceived as relationships, are perceived and operated
>>>>>upon in the relational model in just one common way: as relations.
>>>>
>>>>This is the exact problem Chen identified. In the relational model
>>>>it is impossible to have entity-valued attributes, which, in practice,
>>>>we have a huge amount of.
>>>
>>>Entities are figments of our imaginations.
>>
>> You are an entity.
Date: Fri, 30 Nov 2007 16:24:07 GMT
Message-ID: <HOW3j.48583$eY.13591_at_newssvr13.news.prodigy.net>
Do you pay taxes? Then you are an entity. "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message news:474ebc46$0$5261$9a566e8b_at_news.aliant.net...
> 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 Fri Nov 30 2007 - 17:24:07 CET