Re: Reminder, blatant ad
Date: Mon, 13 Feb 2006 09:29:09 +0200
Message-ID: <dspcg8$ia8$1_at_emma.aioe.org>
"dawn" <dawnwolthuis_at_gmail.com> wrote in message
news:1139620678.347430.274910_at_g43g2000cwa.googlegroups.com...
> > This is not necessarily true for all such systems but in many of those
> What is the test for determining whether they are too tightly coupled?
Look at Codd 1970 ACM paper.
> > the logical and physical model are closely tied together and their
> > efficiency in fact often depends on this close relationship.
> What is it that changes (the "physical model" doesn't resonate with me,
> I want to know what software components would change) that should not
> require a change in the logical model but does in some non-relational
> products? I do not recall ever changing the logical data model in any
> software I have written when a new version of anything was released. I
> do recall changing COBOL code with a new release of Primos in 1977, but
> it was not the logical data model for the indexed sequential files that
> had to change.
He describes various data dependencies:
- ordering dependence
- indexing dependence
- access path dependence
then he introduce "a relational view of data".
Received on Mon Feb 13 2006 - 08:29:09 CET