Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Mon, 27 Jun 2005 22:09:06 GMT
Message-ID: <6O_ve.131771$Vs4.7201818@phobos.telenet-ops.be>

Marshall Spight wrote:
> Jan Hidders wrote:
>

>>It provides you with a higher-level data model.

>
> Can you be specific about some features you consider to
> be higher level?

Let me mention two small things. In the RM if you want to add a one-to-many relationship between two entities you have to extend one of the relations with a foreign key. If there are more than one candidate key you have to choose one of them. In an ER model you don't have to make such a choice, you simply indicate that there is a relationship.

Another small thing is updating primary keys. If a primary key has accidentally been entered wrong and you want to fix that with an update then it is usually not possible to simply update it, and the problem gets even worse if it is also refered to by foreign keys. In an ER model this is a non-problem.

>>Moreover, it has slowly
>>begun to dawn on people that the big advantages of the relational model
>>(simplicity, formal basis, data-independence, declarativity, etc.) are
>>actually also easiliy achieved in other data models.

>
> Do you mean XML here, or are there other specific models you
> have in mind? I'd be interested to look at other models
> that have the features you name, especially simplicity.

I basically have the FDM data model in mind, but modernized a bit.

• Jan Hidders

Received on Mon Jun 27 2005 - 17:09:06 CDT