Re: Pizza Example
Date: Wed, 07 Apr 2004 11:52:29 GMT
"Anthony W. Youngman" <wol_at_thewolery.demon.co.uk> wrote in message
> In message <DIidncafbowjK-_dRVn-uA_at_comcast.com>, Laconic2
> <laconic2_at_comcast.net> writes
> >First, does the relational data model scatter information across
> What do you mean? If you have a repeating attribute, the relational
> model demands that you spread data about a single object across multiple
The argument hinges on the word "about". MV and OO folks would claim that any reference to X is "about" X and therefore should be collected together with everything else "about" X. Relational folks realize that's silly, since these represent different assertions, "about" X ALONG WITH OTHER THINGS.
> >Second, if so, does the database fail to understand what the relational
> >model has done?
> Let's assume we have several types of object. All have repeating
> attributes. And all are related, some by a many-2-many relation. Can a
> relational database group the tables according to the object they
The question is too vague to address - why won't foreign keys suffice in this?
> >And here's a third question: can a relational model be reconstructed
> >the database schema? If not, why not?
> Why not? If you're talking about a Pick schema, then the only reason you
> can't get a relational model is if the Pick designer didn't do his job
> As a Pick database designer, I would have one FILE (our equivalent of
> "table") per real-world object type. The data in this file *is*
> *normalised*. It's just that it's NFNF (non first normal form).
Then it's not normalized. Please, at least use a different term rather than co-opting one already defined. Wait - you used an S in normaliSed. My mistake. :-)
> So. Imagine you've defined a view, in your relational database, that
> joins all tables representing an object. You then "list" (sorry I don't
> know the relational term) one object in your view. In your
> two-dimensional view, imagine that all duplicated values just "don't
What duplicated values? Presumably the "list" (a report) would include a comma-separated representation of the multiple values or some such.
> You now have the equivalent of a Pick RECORD (a bit like your
> row). We don't duplicate a simple attribute because it doesn't make
> sense to do so
In what sense does the relational model duplicate an attribute?
There are multiple values which may be associated with X, but in what sense is it "listed repeatedly"? Again, I don't see the "duplication."