Re: One-To-One Relationships
Date: Mon, 3 Dec 2007 03:05:49 -0800 (PST)
On 2 dec, 16:50, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> 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
> >>>>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?
That depends on which ER dialect you are talking about.
- Jan Hidders