From: OF
To: Editor

Date: 07/25/2003

I want to tell you that your site is wonderful. It helped me so much, and also it is a site that database community really needs. I hope your site grows very much. Please excuse my English, I do not speak it very well.

What happens is that I have seen in Mr. Date's RELATIONAL DATABASE WRITINGS 91-94, that there are some chapters about updating views that are related also to key inheritance. That is why I want to ask you, Mr. Date or Mr. Pascal, about key inheritance: when you have a relation like Parts (from the database Suppliers, Parts and SP) that you project just "city" and "weight", it has no primary key, then in this case a P# is inherited? or maybe a surrogate is generated?.

From: Fabian Pascal

To: OF

Glad we can help. Yes, of course the database community badly needs it--that's why we created it--but whether it appreciates it, is another matter altogether.

A relational projection is defined as one that preserves closure and, thus, the result includes the key.

Courtesy of the relational model, from the source tables and the table operation to create a view, a true RDBMS (TRDBMS) would always be able to know the (inherited) key of the view.

SQL products, of course, do not.

Posted 10/03/03

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