Re: One-To-One Relationships
Date: Sun, 02 Dec 2007 11:50:06 -0400
Message-ID: <4752d432$0$5266$9a566e8b_at_news.aliant.net>
Jan Hidders wrote:
> On 2 dec, 16:10, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
>>Jan Hidders wrote:
>>
>>>On 1 dec, 15:03, JOG <j..._at_cs.nott.ac.uk> wrote:
>>
>>>>[...] let me give an example as to why I find
>>>>the breakdown into entities and relationships deleterious. Say I have
>>>>two entity types staff_members and subjects, and a relationship
>>>>teaches:
>>
>>>>staff_member -- teaches --> subject
>>
>>>>This is all good and fine until a requirement changes that we need to
>>>>record the day the lecture is given on.
>>
>>>Yes. Relationships may become Entities, Roles may become
>>>Relationships, Attributes may becomes Relationships, etc. As David
>>>remarked, there are ER dialects like ORM that smoothen this a bit, but
>>>you can never make that really go away. These problems have
>>>counterparts in the RM where foreign keys may become tables by
>>>themselves, or tables are split because a one-to-one relationship has
>>>become a one-to-many one.
>>
>>ORM = ER ?!? Since when?
> > Since the objects and the fact-types in ORM are basically the same > thing as entities and relationships in ER.
Basically the same? Or the same? Received on Sun Dec 02 2007 - 16:50:06 CET