Re: More on identifiers
Date: Sat, 6 Jun 2009 03:24:17 -0700 (PDT)
On Jun 6, 12:19 pm, "Joe Thurbon" <use..._at_thurbon.com> wrote:
> On Fri, 05 Jun 2009 14:52:27 +1000, David BL <davi..._at_iinet.net.au> wrote:
> > Due to the projection, all the abstract identifiers have disappeared
> > from every relation. In a way, it's like seeing a database within a
> > database! The value of the "inner" database records all the facts in
> > the /context/ of just one of the items, and therefore has no need for
> > abstract identifiers to glue things together.
> I may have misunderstood, but haven't you just moved the 'problem'?
I don't understand what you mean.
> is, each abstract identifier that you want to get rid of ends up with 'its
> own database'.
Yes, the intention is to eliminate the abstract identifiers from the logical model, by instead using a database /value/ as a descriptor for each item. This value is only a function of the recorded visible properties of the item.
> Two database values that came from entities that differed
> only by their abstract identifier will not be distinguishable.
That is a good thing! It means that two items that are indistinguishable in terms of the /recorded/ visible properties have the same descriptor value.
> So to
> distinguish between them, the abstract identifiers and up being arbitary
> names of databases.
The idea is not to distinguish them. That's an advantage of completely eliminating the abstract identifiers from the logical model by using DVAs. If there are duplicates then the "outer" database can record the number of duplicates. Of course more generally the descriptors could take part in all sorts of relations in the "outer" database.
A binding between a name and a value can be regarded as a variable (something that "holds" or "encodes" a value). The elimination of abstract identifiers can be regarded as the elimination of variables from the logical model.
Thanks Received on Sat Jun 06 2009 - 12:24:17 CEST