Re: One-To-One Relationships
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 acm.org). The sarcasm of the second one made me laugh.
From the first chapter:
<quote>
From chapter 30:
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>
<quote>
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