Hello John, (01)
On Thu, Oct 11, 2012 at 11:18:45AM -0400, John F Sowa wrote:
> People understand AND, OR, NOT, and EXISTS -- and their combinations.
> They can be evaluated in polynomial time in all SQL implementations.
> But nobody, not even the SPARQL developers, understand FILTER, OPT,
> and UNION. They're still publishing papers to show that combining
> them makes the evaluation NP complete. (02)
Yes. It is my impression from working with SPARQL and SQL that constructing
and optimizing SPARQL queries is more difficult than SQL. (03)
> Furthermore, triple stores are just a particular implementation.
> Note Michael Stonebreaker's publications about NOSQL (in the sense
> of Not Only SQL). He has an extremely fast implementation that uses
> the same optimizations as triple stores, but he extends them to
> support relations with any number of arguments. (04)
I will not read those papers because they are behind a paywall. We all know
that nary relations can be modeled with binary relations so what reasons could
there be for nary relations ? I see those potential reasons: (05)
1) Simplicity of notation
2) Efficiency of computation (lookup, store)
3) Efficiency of reasoning (06)
So you see any other ? (07)
RDBs are efficient because if you have one column of a row, the others are
often stored nearby. This is possible because the schema is fixed and I have
no idea how Michael Stonebreaker would be able to avoid multiple lookups with
general n-tuples. (08)
Maybe reason 2) and 3) will go away because n-tuples cannot be made efficient
in the general case or because the computers get fast enough (I know you think
that the needs will grow faster than the performance). But how important is
reason 1) ? (09)
Regards, (010)
Michael Brunnbauer (011)
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