Thanks Dave for your answer.
I need to use a RETE engine since I want it to infer « live » when I add new
triples in the graph. So it seems to me that forward_rete is the only option
for that. Other options recheck the full graph to recompute inferences, right ?
Based on your answer, it seems that I now have 2 choices :
1. try to patch the RETE engine
2. try to start developing a brand new rete-like engine, probably less
memory consuming, but probably also slower than the existing one.
Chris.
Le 7 mars 2014 à 13:00, Dave Reynolds <[email protected]> a écrit :
> On 07/03/14 10:36, Christophe FAGOT wrote:
>> Hi there,
>>
>> I’m actually using Jena in forward rete configuration, with Jena 2.11.1. If
>> I use some very simple rules like the following, the memory used by my JVM
>> becomes huge with few statements (around 100Mo for only 3500 statements). I
>> ran a simple test in which instances and data property values were always
>> different, in order to avoid combinatorial combinaisons.
>>
>> The sample rule :
>>
>> [rule: (?instance rdf:type test:Instance),
>> (?object rdf:type test:Object),
>> (?instance test:instanceAge ?age),
>> (?object test:objectAge ?age),
>> ->
>> (?instance test:isLinked "true"^^xsd:boolean)]
>>
>> Does anyone see a reason for such huge memory space required by the RETE
>> engine ? Any workaround to use ?
>
> It's due to the crudeness of the Jena RETE implementation.
>
> It is in effect doing (pseudo-notation):
>
> (?instance rdf:type test:Instance)
> (?object rdf:type test:Object)
> (?instance test:instanceAge ?age1)
> (?object test:objectAge ?age2)
> (= ?age1 ?age2)
>
> So that it builds a queue of all possible instance/object pairs before the
> final join on age.
>
> Which means that queue ends up as N(objects) * N(instances) long. So
> quadratic rather than combinatorial but that's enough for the blow up.
>
> Can't think of a work around.
>
> If you can use backward rules instead of RETE that should help.
>
> The RETE engine could certainly be improved (patches welcome). Though the
> looooong term best option might be to consider phasing out both the existing
> rule engines in favour of something simpler and more scalable. Not something
> I could personally contribute to right now.
>
> Dave
Christophe FAGOT, PhD - Product owner, informatique
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