Re: One-To-One Relationships

From: paul c <>
Date: Tue, 30 Oct 2007 17:19:18 GMT
Message-ID: <qIJVi.161465$th2.107000_at_pd7urf3no>

paul c wrote:
> David Cressey wrote:

>> I hope this isn't too nit picky.  I think the distinction between what 
>> you
>> discover via analysis and what you create during implementation 
>> (following
>> design)  is very fundamental,  and needs to be kept clear in all our
>> discussions.

> I don't think it's too nit picky at all. I wish the OP had given an
> example because I think people here are talking about two different
> things as you suggest, ie., a one-to-one as the ER people would see it
> (eg., dept has one mgr and mgr has one dept) versus a relation that
> somebody wants to make into two relations.

Regarding ER, here are some quotes from Codd's book (available for free at The sarcasm of the second one made me laugh.

 From the first chapter:

About six years after my first two papers on the relational model [Codd 1969 and 1970], Chen [1976] published a technical paper describing the entity-relationship approach to database management. This approach is discussed in more detail in Chapter 30, which deals with proposed alternatives
to the relational model. Although some favor the entity-relationship approach, it suffers from three fundamental problems: 11 Only the structural aspects were described; neither the operators upon these structures nor the integrity constraints were discussed. Therefore, it was not a data model.
2. The distinction between entities and relationships was not, and is still not, precisely defined. Consequently, one person's entity is another person's relationship.
3. Even if this distinction had been precisely defined, it would have added complexity without adding power.
Whatever is conceived as entities, and whatever is conceived as relationships,
are perceived and operated upon in the relational model in just one common way: as relations. An entity may be regarded as inter-relating an object or identifier of an object with its immediate properties. A relationship
may be regarded as a relation between objects together with the immediate properties of that relationship. <end quote>

 From chapter 30:
Of the five
approaches discussed in this chapter, this one is clearly the winner in terms
of its lack of precise definitions, lack of a clear level of abstraction, and
lack of a mental discipline. The popularity of ER may lie in its multitude of interpretations, as well as its use of familiar but obsolete modes of thought.
<end quote> Received on Tue Oct 30 2007 - 18:19:18 CET

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