On Feb 1, 2009, at 1:55 PM, John F. Sowa wrote:
> There are horror stories about large RDB systems in the US that
> were "mandated" to be translated to RDF with disastrous results.
> (01)
Can you expand on this? I have not heard any such horror stories
related to RDF. It would be remarkable, as the RDF specs were only
published four years ago. (02)
> The basic issue is that RDBs use indexes to find the relevant
> data in logarithmic time. When the index cannot be used because
> it is necessary to process an entire column, the RDB pages the
> data in an orderly fashion.
>
> The problem with SPARQL is that RDF is not designed to support
> indexing. The people who built so-called "triple stores" say
> that they're efficient because they run in RAM. (03)
For some purposes, they outperform databases by being implemented via
hash tables, giving in effect constant rather than logarithmic access
time. But performance is influenced by the statistics of the triples
in use, to be sure. (04)
> But any DB that
> fits in RAM is a toy. (05)
Not any longer. Laptops, and even some cell phones, now routinely use
64-bit address spaces, and a gigabyte of RAM costs around $50. The
complete Cyc ontology fits into a laptop. By next year I expect to
trade my disc drive for a flash disc, giving my Powerbook around 300
gig of close-to-RAM-speed memory without any moving parts. (06)
> If you take a non-toy DB and map it to
> RDF, it doesn't fit in RAM. Furthermore, those triples aren't
> indexed, and they're not designed to be paged in an orderly
> fashion. The result is endless disk thrashing. (07)
Who says the triples aren't indexed? It all depends on how your
software is implemented. Bad software will thrash whether its using
RDB, RDF or anything else. (08)
> If I had a pointy-haired boss who mandated the translation
> of an RDB to RDF, I would immediately send my resume to every
> reasonable employer (09)
Me too, but only because bosses shouldn't be mandating engineering
decisions. (010)
Pat (011)
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