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_at_news.aliant.net>
>
> 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?
Date: Fri, 30 Nov 2007 19:38:00 -0400
Message-ID: <47509edb$0$5267$9a566e8b_at_news.aliant.net>
paul c 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? >> [Quoted] >> 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?
[Quoted] Shhhh. Someone will imagine a singleton entity. Received on Sat Dec 01 2007 - 00:38:00 CET