Re: One-To-One Relationships

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 30 Nov 2007 19:38:00 -0400
Message-ID: <47509edb$0$5267$9a566e8b@news.aliant.net>

paul c wrote:

> Bob Badour wrote:
>

>> paul c wrote:
>>
>>> Tegiri Nenashi wrote:
>>>
>>>> On Nov 30, 1:44 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
>>>>
>>>>> On 30 nov, 19:45, "David Cressey" <cresse..._at_verizon.net> wrote:
>>>>>
>>>>>> Here's the way I would try to unify the two concepts.  
>>>>>> Relationships can be
>>>>>> binary, ternary, and so on,  depending on the number of entities 
>>>>>> involved in
>>>>>> a single instance of the relationship.  How about considering an 
>>>>>> entity a
>>>>>> "unary relationship"?
>>>>>
>>>>> Minor nitpick: that unary relation is the entity type (or class or
>>>>> whatever you want to call it), not the entity itself, which is of
>>>>> course the thing for which the unary relationship holds. Otherwise you
>>>>> are of course completely correct.
>>>>
>>>> So the matter reduces to relation attribute counting? Then, what
>>>> additional insight the "new" concepts of "entities" and "relationship"
>>>> add to the "relation" and "domain"?
>>>
>>> How do relations with no attributes unify?
>>
>> Who said relations unify?

>
> Just echoing David C, could have asked how relation concept unifies with
> entity concept when a relation has no attributes, or what is the ER
> equivalent for no attributes? eg., how would you draw it, would it be
> some kind of something-to-zero relationship? But "zero-"what?

Shhhh. Someone will imagine a singleton entity. Received on Fri Nov 30 2007 - 17:38:00 CST