Re: One-To-One Relationships
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 30 Oct 2007 14:26:20 -0300
Message-ID: <4727693d$0$14855$9a566e8b_at_news.aliant.net>
>
> ...
>
>
> Regarding ER, here are some quotes from Codd's book (available for free
> at acm.org). The sarcasm of the second one made me laugh.
>
>
> From the first chapter:
>
> <quote>
> 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:
> <quote>
> 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>
Date: Tue, 30 Oct 2007 14:26:20 -0300
Message-ID: <4727693d$0$14855$9a566e8b_at_news.aliant.net>
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 acm.org). The sarcasm of the second one made me laugh.
>
>
> From the first chapter:
>
> <quote>
> 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:
> <quote>
> 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>
Sadly, neither the familiarity nor the obsolescence have changed and neither are they likely to. Received on Tue Oct 30 2007 - 18:26:20 CET