Re: One-To-One Relationships
Date: Fri, 30 Nov 2007 11:25:15 -0400
>>"paul c" <toledobythe..._at_ooyah.ac> wrote in message
>>>Bob Badour wrote:
>>>>David Cressey wrote:
>>>>>"Bob Badour" <bbad..._at_pei.sympatico.ca> wrote in message
>>>>>>Entities are figments of our imaginations.
>>>>>You are an entity.
>>>>Am I? Or am I billions of cellular entities? Or am I part of a larger
>>>I can't imagine how to store an entity. When I hear of it having been
>>>done, I just pretend I heard tuple instead, even though I admit I can't
>>>imagine how to actually store a tuple. All I know how to do with a
>>>machine is mimic assignment. I think Codd was prepared to exclude
>>>As far as a db model goes, entities seem to have use only as
>>>conversational devices, as you implied and as David C demonstrated!
>>>Tuples might not seem any better, but at least we can imagine how they
>>>are applied by operators.
>>Your comment goes back to discussions we've had concerning modeling and
>>design going back years in this newsgroup. I'm going to repeat things I've
>>When I first learned database design, the way I learned it was three level:
>>conceptual modeling, logical modeling and design, and physical design.
>>For historical clarity, I learned this in about 1984. I will not claim
>>that it was "leading edge" at the time.
>>The ER model was used for conceptual modeling. The "entities" and
>>"relationships between entitities" discussed in the ER model are not (in
>>this context) stored in the database. They are entities and relationships
>>that exist in the real world, at least in the mind of the subject matter
>>experts. The data values to be stored and delivered by the database
>>describe these entities and relationships. The entire model serves to
>>discuss the information requirements with SMEs, clients, even prospective
>>users, without getting specific about what form they are going to take when
>>stored or when presented.
>>Tuples don't get mentioned in the ER and this is intentional. The database
>>design is not bound, at this point in time, to a relational design.
> > > This is interesting David. Perhaps it infers the distinction (which I > christen henceforth as Jim's law): > > ENTITY PROPONENT: Does not believe a particular conceptual model > should not bound to a specific logical one. > TUPLE PROPONENT: Does not believe a particular logical model should be > bound to a single conceptual one. > > Any takers?
What is the purpose of mixing levels of discourse?
I am not a fan of entities because I think E-R is a piss-poor way of conceptual modeling. Pictorial representations are crutches that interfere with effective thought. Even in simple highschool mathematics, graphical analysis is full of pitfalls and leads to unecessary special case analysis.
Any analytic method based on imagined distinctions is flawed to its core. Received on Fri Nov 30 2007 - 16:25:15 CET