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From Dave Reynolds <>
Subject Re: [GenericRuleReasoner] inner workings
Date Wed, 13 Mar 2019 11:10:56 GMT
Hi Marco,

Not a "consensus" that I'm part of so not something I could comment on.


On 13/03/2019 10:49, Marco Neumann wrote:
> correct if me if I am wrong but from my vantage point I seem to notice
> a silent consensus in the RDF community to go from SPIN rules to SHACL
> which now comes with its own SHACL rule engine [1].
> The new SHACL efforts are mostly guided by TopQuadrant and a change
> from the initial layered approach to go with SPARQL RDF
> (SPIN+(SHACL-rules)). So I presume the current game plan is that SHACL
> will "rule" them all in the end.
> If so it would be nice to have a feature list for SHACL rules. And
> does this mean it will be rules without validation and just CONSTRUCT
> queries or are the rule semantic restrictions build into SHACL? I am
> sure this will work fine for many use cases we have but since we are
> starting to blur the lines between rules/reasoner/sparql would be nice
> to have some general autoritative clarification here.
> [1]
> On Wed, Mar 13, 2019 at 10:14 AM Dave Reynolds
> <> wrote:
>> Hi Marco,
>> Sorry, I'm not aware of other rule engines having been wired to Jena but
>> that doesn't mean it hasn't been done. In particular I'm surprised
>> there's not a drools-for-jena project somewhere. People have certainly
>> experimented with that, even written papers comparing performance [1],
>> but I'm not aware of any supported tooling.
>> Dave
>> [1]
>> On 12/03/2019 22:18, Marco Neumann wrote:
>>> so what's your current recommendation for a superior third party rules
>>> reasoner that works efficiently with the jena tooling? free & commercial
>>> option welcome
>>> Marco
>>> On Mon 14. Jan 2019 at 19:16, Dave Reynolds <>
>>> wrote:
>>>> Hi Barry,
>>>> [Agreed that dev is probably the better place to discuss this.]
>>>> The two engines in jena are indeed loosely styled on RETE and on tabled
>>>> datalog. However, I wouldn't claim they were particularly complete or
>>>> good implementations of either. So while looking at some of the source
>>>> literature that inspired them might be helpful don't expect very much of
>>>> what's covered in the literature to be present in the code.
>>>> For RETE then the wikipedia article [1] is a good summary and source of
>>>> starting references. I had a copy of the original Forgy paper [1](ref
>>>> 1), among others,when I was doing the work. There has been a *lot* of
>>>> work on improvements to RETE since the 80s and while there were times
>>>> when we might have done a new forward engine using more modern
>>>> techniques it never happened.
>>>> For the backward engine the approach is a variant of SLG-WAM as used for
>>>> XSB but highly highly simplified since we can't express general tuples
>>>> or recursive data structures within jena's triples. A few google
>>>> searches haven't turned up the exact paper that originally inspired the
>>>> approach. The closest I've found are [2] and [3], which probably cover
>>>> the same ground.
>>>> Let me reinforce that the Jena engines are really simplified. They were
>>>> enough to get the job done at the time (over a decade ago now) and have
>>>> proved useful for some people since but I wouldn't want to defend any of
>>>> the implementation choices.
>>>> Dave
>>>> [1]
>>>> [2]
>>>> [3]
>>>> On 14/01/2019 16:33, ajs6f wrote:
>>>>> I have no useful general information about the reasoning framework, but
>>>> I am copying this over to dev@. Discussions of how to extend Jena
>>>> definitely have a place there.
>>>>> ajs6f
>>>>>> On Jan 14, 2019, at 6:40 AM, Nouwt, B. (Barry)
>>>> <> wrote:
>>>>>> Hi all, I want to investigate the inner workings of the
>>>> GenericRuleReasoner (with the purpose of extending it in the future). In
>>>> Jena's documentation I read:
>>>>>> "Jena includes a general purpose rule-based reasoner which is used
>>>> implement both the RDFS and OWL reasoners but is also available for general
>>>> use. This reasoner supports rule-based inference over RDF graphs and
>>>> provides forward chaining, backward chaining and a hybrid execution model.
>>>> To be more exact, there are two internal rule engines one forward chaining
>>>> RETE engine and one tabled datalog engine - they can be run separately or
>>>> the forward engine can be used to prime the backward engine which in turn
>>>> will be used to answer queries."
>>>>>> source:
>>>>>> Apart from Jena's documentation, Jena's mailing lists and its source
>>>> code, are there any resources that can better help me grasp what is
>>>> happening inside the generic rule reasoner? For example, the text above
>>>> mentions the forward chaining RETE engine and the tabled datalog engine,
>>>> are there any scientific papers that I might read to better understand
>>>> their inner workings?
>>>>>> Maybe this question is better suited for the
>>>> <>?
>>>>>> Regards, Barry
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> --
> ---
> Marco Neumann

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