Re: One-To-One Relationships
From: paul c <toledobythesea_at_ooyah.ac>
Date: Fri, 30 Nov 2007 23:24:52 GMT
Message-ID: <8Z04j.8729$UQ1.765_at_pd7urf1no>
>> Tegiri Nenashi wrote:
>>
>>> On Nov 30, 1:44 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
>>>
>>>> On 30 nov, 19:45, "David Cressey" <cresse..._at_verizon.net> wrote:
>>>>
>>>>> Here's the way I would try to unify the two concepts.
>>>>> Relationships can be
>>>>> binary, ternary, and so on, depending on the number of entities
>>>>> involved in
>>>>> a single instance of the relationship. How about considering an
>>>>> entity a
>>>>> "unary relationship"?
>>>>
>>>> Minor nitpick: that unary relation is the entity type (or class or
>>>> whatever you want to call it), not the entity itself, which is of
>>>> course the thing for which the unary relationship holds. Otherwise you
>>>> are of course completely correct.
>>>
>>> So the matter reduces to relation attribute counting? Then, what
>>> additional insight the "new" concepts of "entities" and "relationship"
>>> add to the "relation" and "domain"?
>>
>> How do relations with no attributes unify?
>
> Who said relations unify?
Date: Fri, 30 Nov 2007 23:24:52 GMT
Message-ID: <8Z04j.8729$UQ1.765_at_pd7urf1no>
[Quoted] 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?
[Quoted] 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? Received on Sat Dec 01 2007 - 00:24:52 CET