From: GA

To: Editor

 

I've been reading the articles posted by Mssrs. Pascal and Date with great interest and relish. I am one of those "whose heart is in the right place", but whose grasp is still in development. I have a single, if not simplistic, question:

 

You constantly remind us that the relational model is a logical model having no connection to any physical model (so I infer). You also indicate how no commercial product fully implements the relational model.

 

Therefore, how do we make use of the relational model when dealing with the physical constructs of a commercial database program (Oracle, Access, DB2, etc.)?

 

 

From: Fabian Pascal

To: GA

 

Here's an extract from my reply to a critic, forthcoming at DMDirect:

 

“A common criticism of the relational model is that it is not practical because it “does not address” physical implementation, while in reality this is a huge practical advantage.

 

Codd's Rule 8, Physical Data Independence: Interactive applications and application programs should not have to be modified whenever changes in internal storage structures and access methods are made to the database.

 

Note that how products should achieve this is not specified, and no specific physical implementations are imposed, or prohibited. The relational model is nothing but logic applied to databases, and logic has nothing to say about physical implementation. Moreover, as I explained in my article, this is a major relational advantage, because it leaves implementers free to do whatever they darn please at the physical level to maximize performance, as long as they do not expose it to users in applications. It follows that any performance problem encountered in practice cannot possibly be due to the relational model, or to the relational nature of a DBMS. It is a product implementation issue by definition.

 

Posted 01/03/03

 

 

 

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