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<div>Seth Ladd is asking what is the 
<a href="http://www.picklematrix.net/archives/000983.html">Best
Reasoner Available?</a> There are some very good issues raised in
his post, which more or less starts with: "ok we've got the RDF
storage 
(Oracle 10g) - now what?"
One big question is whether Semantic Web applications need
reasoners. I'm sure this will vary from case to case. The first
kind of situation that springs to mind is a 'pure' SemWeb app, one
which depends heavily on the logic, e.g. an expert system using
something like the 
<a href="http://www.schemaweb.info/schema/SchemaDetails.aspx?id=62">Wine
Ontology</a>. At the opposite extreme there will be case where no
inferencing is needed (or realistic), for instance when a company
already has its data in a regular RDBMs, with the business logic
being expressed through a combination of SQL and object code. The
RDF/OWL expression of the data would then effectively be a
view.
But back to Seth's situation, where you do have a triplestore. I
honestly have no idea in the situation where you have a largish
amount of data and want full inferencing. Coincidentally I was
chatting about this over the weekend with 
<a href="http://www.langreiter.com/">Chris Langreiter</a>. I
couldn't think of any largish scale triplestore that had built-in
RDFS and/or OWL reasoning, unless Jena's OntModel can be
persistent. (Hmm, using the 
<a href="http://dig.sourceforge.net/">DIG</a> interface to
reasoners, presumably you'd have to tell them all the statements,
which might be tricky if you're talking millions of
triple…)
Around this space there are questions of whether the store
should do eager or lazy evaluation of the inferences - 
<code>think</code> when you add triples or when you look for them.
Eager would presumably be easiest to implement, but likely suffer
from issues due to the increased number of triples present. I'm not
really sure how one would manage lazy evaluation of queries in an
efficient way that would still be complete. Can tableaux do this?
Or maybe a graph path walking approach something along the lines of

<a href="http://www.agfa.com/w3c/jdroo/">Jos De Roo</a>'s 
<a href="http://www.agfa.com/w3c/euler/">Euler</a> might do the
trick.
I can say from experience that a non-reasoning RDF store can be
very useful, especially used an agile replacement for a regular
relational DB. I've also found limited reasoning very valuable -
just using MortenF's 
<abbr title="Inverse Functional Property">IFP</abbr> 
<a href="http://rdfweb.org/topic/Smushing">smusher</a> with Redland
made a huge difference to the capabilities (capabilities that can
be considered built-in, rather than hanging off in separate
arbitrary code).

 In the forseeable future on the Web at large I think it
 likely that non- or just minimal-inferencing RDF stores will make
 up the majority, analogously to the way most
 databases/filesystems behind current sites aren't particularly
 smart.

Seth also asks more generally about SemWeb app architecture. I
guess we need a Patterns book… 
As it happens I've got a longish post in the pipeline for one
such kind of setup (content-oriented).
Anyhow, go read Seth's post (and cc me with comments
;-)[Danny]
</div>