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

Alexandr Savinov wrote:
> Here is even simnpler example. Assume you have a number of departments.
> There is two ways how you can represent them:
> 1. As records in a table of departments
> 2. As individual tables (possibly with support from one common
> meta-table from #1 as you noticed because relational model does not
> allow for tables to have fields and to be used as entities)

#1 is the right way
#2 is the wrong way

> It is very general and wide spread trade off and it is important to
> recognize that there is such an alternative (but it is prohibited to
> think so in RM).

What would be the benefits of approach #2? The drawbacks are obvious enough. How would you express a relationship between departments with approach #2? Or associate employees with departments?

> Another aspect of this problem. A schema is not part of the relational
> model but it is heavily used in complex applications. You know that any
> implementation has a table of tables and it is reflects the fact that
> tables are rows and have normal properties. Thus practice also confirms
> my hypothesis however currently there is no a data model (theory) for that.

I'm not sure what you mean by this. AFAIK it has always been the case that we would expect that the relational schema (metadata) would itself be defined in relations in the form of the "system catalog". No new theory is needed, since it is just another application of the relational model. Received on Tue Jun 07 2005 - 15:29:49 CEST