Re: Newbie question about db normalization theory: redundant keys OK?
Date: Sat, 22 Dec 2007 13:17:06 GMT
"Frank Hamersley" <terabitemightbe_at_bigpond.com> wrote in message
> David Cressey wrote:
> > "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> > The question arises whether the database communicates any data other
> > the data contained in its state. I'm going to pull a quote from Codd's
> > paper. Even though this quote is about consistency, rather than
> > I want to draw your attention to the wording.
> > "It is important to note that consistency as defined above
> > is a property of the instantaneous state of a data bank, and
> > is independent of how that state came about. Thus, in
> > particular, there is no distinction made on the basis of
> > whether a user generated an inconsistency due to an act of
> > omission or an act of commission. "
> Interesting - I had always assumed that Codds use of "time varying" had
> implied temporality but the above quote must weaken that view.
It's my understanding, from reading in here, that "time varying relation"
was basically the same thing as "relational variable", which in turn gets
abbreviated to "relvar".
It's my understanding that a consistent view of a database involves
everything written by prior transactions and nothing written by concurrent
transactions, let alone future transactions. Concurrency is, of course,
more complicated than this, but this is sufficient for this discussion.
It's my understanding that a consistent view of a database involves everything written by prior transactions and nothing written by concurrent transactions, let alone future transactions. Concurrency is, of course, more complicated than this, but this is sufficient for this discussion.
I have preferred to think of the database data structures as "containers" rather than "variables". The contents of containers are presumably time varying, subject to the above comment on transactions. I suppose you could have a WORM container that, once written, remains constant, but I never thought of that until just now.
The "container" terminology makes for a nice distinction between container based addressing and content based addressing. This in turn leads to the distinction between the graph model of data and the relational model of data. But, AFAIK, it's just terminology. If there's any deep thought here, it isn't my thought. Received on Sat Dec 22 2007 - 14:17:06 CET