Re: Has E/R had a negative impact on db?

From: Jan Hidders <>
Date: 24 Apr 2006 06:44:43 -0700
Message-ID: <>

JOG wrote:
> Just a thought.

Likewise. :-)

> I don't like entities. In fact I despise entities, as the enemy of good
> information philosophy. You see I just don't accept their existence.

Actually, I don't see what you could possibly mean with that, and to the extent that I can guess a meaning I find that a rather baffling statement. The usual definition of 'entity' in the context of data modelling for database is something like "things that can be identified and which we would like to store information about in the database". If that's how I interpret your statement then you seem to be saying that you don't believe there are such things, and since we cannot store information about things we cannot identify, this leads inexorably to the conclusion that you don't believe that we can store information about anything interesting in a database.

Yes, I have just put words in your mouth, but you shouldn't have left a hole there. :-) If you are going to rant about something you despise, you better define it properly.

> There is no magical wrapper surrounding some construct that turns it
> into a nicely formed 'thing' or 'object'.

What makes you think a wrapper is needed?

> Sure, we can invent them, but
> there is never any inherent truth to their boundaries.

When making an ER / ORM / ... some ER dialect ... model one doesn't identify boundaries, except perhaps when determining part-of relationhips, so I have no idea what you are talking about here. Until you further explain this it looks mainly like pseudophilosophical nonsense to me.

> To me the situation get worse when one then adds relationships between
> entities. What on earth is the difference between an entity (an
> association of attributes) and a relationship (an association of
> entities), except for the fact that a relationship is constrained to
> being binary.

What makes you think a relationship is necessarily binary? And why do you think it is a problem that the distinction between relationsips and entities is not clear? Does it also bother you that the distinction between a relation and a foreign-key relationship is not always clear? Or between a unary relation and a domain?

> Nothing. In fact all they are, are special cases of n-ary
> relationships, or 'associative entities'.

No, that is clearly false. Not every entity is necessarily identified by its associated attributes, identification could be more complex and/or indirect than that.

> Now Codd grokked this. I am sure he did. That's why the RM has no
> 'links' and pivots on the information principle.

Codd is not on you side here. The surrogate identifiers qualify as "links" and why, if he thought the term "entity" meaningless, did he use it?

> Okay, so for those in the know this isn't an issue and E/R is a useful
> tool. But for those not in the know (which appears to be a lot of the
> industry) it promotes the fallacy of the Entity/Relationship
> distinction, of impenetrable wrappers, and encourages the mindset that
> has lead to OODBMS, XML databases, etc.

Gee, James, here I was thinking I was in the know and it turns out that I couldn't disagree more, so apparently I'm not(!) I would argue that it is exactly *because* ER dialects were ignored as a viable alternative for a DBMS logical model, and consequently got swallowed up and crushed in the OODBMS avalanche, that the field of database theory has been held back. Serious study of object / entity identity would have led to simpeler and more general models, and we would have had a better understanding of schema evolution and temporal databases.

  • Jan Hidders
Received on Mon Apr 24 2006 - 15:44:43 CEST

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