Re: Trying to define Surrogates

"David Cressey" <dcressey_at_verizon.net> wrote in message news:KShGg.1199$HW1.451_at_trndny03...
>
> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> news:760Gg.9898$1f6.4300_at_newssvr27.news.prodigy.net...
>> I've changed my position. I just had a revelation that the need for key
>> stability is a symptom of the problem, not the problem itself. I still
>> think that the model has a problem, but the root cause has nothing to do
>> with how stable a key is: rather, it is that there isn't a mechanism
> defined
>> in the model to correlate tuples during an update. I posted in the other
>> thread the line of thinking that led to this revelation, but I'm going to
>> repost, so that others who are not following that thread can comment.
>> I'm
>> going to use the subject "Relation Schemata vs. Relation Variables" if
> you'd
>> like to follow it.
>
>
> The minute you start "correlating tuples" instead of correlating the
> things
> the data describes you are starting down the path of reducing the RDM to
> the GDM. (graph data model). Tuples aren't correlated. Data items are.
>
I see your point, but I don't agree. If tuples CAN be correlated, then they don't just represent facts, they must instead represent facts about things that can change their appearance without changing their identity. There are two ways to be sure that something that you talked about before a change is the same as what you're talking about now. One is to choose a set of identifying properties of the thing that you can be certain will remain constant throughout the change, and the other is to observe it throughout the change, noting how it changed. In the context of a database, you can choose identifying properties of each thing that are certain to remain constant throughout the change and reference them in the facts about the thing, or you can observe the things that are changing, noting how each changed.

>
>
Received on Mon Aug 21 2006 - 20:27:55 CEST