On Dec 20, 2009, at 3:49 PM, Jeffrey Schmitz wrote:
> Just a quick point before I look into how to use union graphs.
>
> The SDB backed model I was using wasn't an OntModel, it was just
> produced by copying the OntModel into it. e.g.
>
> _store = SDBFactory.connectStore("sdb.ttl");
> Model _sdbModel =
> SDBFactory.connectNamedModel(_store, URI);
> _sdbModel.add(ontModel)
>
> but it seemed to still be much slower than just using a purely in
> memory model.
Sure. Of course any DB-backed solution will be slower than an in-memory one.
You can work around some slowness with careful engineering. For example,
- compute the class-to-rule mapping only once (walking the SPIN RDF syntax
expressions might be slow on a DB).
- if there are no cycles in your rules, then the inferred triples can be
written to an in-memory model to prevent many small update requests.
- use named graphs to physically store all relevant sub-graphs in the same SDB.
Then SDB can build a shared index for the whole union graph, which you can then
query with best performance.
- use TDB as a local cache that is mirrored with an SDB. This will boost
performance because TDB will (esp on 64 bit) do smart caching so that most
operations are in fact done in memory. You can synchronize any write operations
with GraphListeners into the underlying SDB.
>
> Since the only reason for me to persist the inferred models would be
> for debugging, I think using the memory only inference models (with an
> option to make them SDB backed) may be the way to go. The drawback
> will be that I'll have to re-generate the inference models on any
> change to the SDB backed "base" model, right?
>
> So, right now I'm thinking of managing the following three Models (not
> OntModels) during runtime for each "A-Box" model that needs to be
> persisted .
>
> 1. A SDB backed baseModel that just contains the A-Box model triples
> 2. A memory only memModel that is basically a copy of an OWL_MEM
> OntModel based on the baseModel, with possibly some specially selected
> SPIN inferences.
> 3. A memory only infModel that is a copy of the memModel, plus all the
> generalized SPIN Inferences (mainly those attached to OWL:Thing).
>
> Any comments on this approach?
If you have partitioned your model into sufficiently small chunks, then you
could save many small transactions by doing a batch copy of the whole named
graph into a memory model for inferencing. In general though I think you may
want to look into using TDB (in conjunction with SDB) to get the best of both
worlds.
BTW I have clarified the contract of the init method (see your other message).
It does not require an OntModel, but any Model that contains the relevant
triples (e.g. in a separate named graph).
Holger
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