On Tue, Nov 08, 2005 at 02:14:58PM -0500, John D. Burger wrote:
> Evandro's mailing lists (Please, don't send personal messages to this
> address) wrote:
>
> >It has nothing to do with normalisation.? It is a program for
> >scientific applications.
> >Data?values are broken into column to allow multiple linear regression
> >and multivariate regression trees computations.
>
> Having done similar things in the past, I wonder if your current DB
> design includes a column for every feature-value combination:
>
> instanceID color=red color=blue color=yellow ... height=71
> height=72
> -------------------------------------------------
> 42 True False False
> 43 False True False
> 44 False False True
> ...
>
> This is likely to be extremely sparse, and you might use a sparse
> representation accordingly. As several folks have suggested, the
> representation in the database needn't be the same as in your code.
>
> >Even SPSS?the most well-known statistic sw uses the same approach and
> >data structure that my software uses.
> >Probably I should use another data structure but would not be as
> >eficient and practical as the one I use now.
>
> The point is that, if you want to use Postgres, this is not in fact
> efficient and practical. In fact, it might be the case that mapping
> from a sparse DB representation to your internal data structures is
> =more= efficient than naively using the same representation in both
> places.
s/Postgres/just about any database/
BTW, even if you're doing logic in the database that doesn't mean you
have to stick with the way you're representing things. There's ways to
get the same info via conventional SQL that doesn't involve building a
huge crosstab.
Something interesting is that the data structure presented here looks a
hell of a lot like a bitmap index, something new in 8.1 (well, at least
bitmap index scans).
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461