Combining RDFS/OWL with custom rules
Sometimes one wishes to write generic inference rules but combine them with some RDFS or OWL infernece. With the current Jena architecture limited forms of this is possible but you need to be aware of the limitations.
There are two ways of achieving this sort of configuration within Jena (not counting using an external engine that already supports such a combination).
Firstly, it is possible to cascade reasoners, i.e. to construct one InfModel using another InfModel as the base data. The strength of this appoach is that the two inference processes are separate and so can be of different sorts. For example one could create a GenericRuleReasoner whose base model is an external OWL reasoner. The chief weakness of the approach is that it is "layered" - the outer InfModel can see the results of the inner InfModel but not vice versa. For some applications that layering is fine and it is clear which way the inference should be layered, for some it is not. A second possible weakness is performance. A query to an InfModel is generally expensive and involves lots of queries to the data. The outer InfModel in our layered case will typically issue a lot of queries to the inner model, each of which may trigger more inferenece. If the inner model caches all of its inferences (e.g. a forward rule engine) then there may not be very much redundancy there but if not then performance can suffer dramatically.
Secondly, one can create a single GenericRuleReasoner whose rules combine rules for RDFS or OWL and custom rules. At first glance this looks like it gets round the layering limitation. However, the default Jena RDFS and OWL rulesets use the Hybrid rule engine. The hybrid engine is itself layered, forward rules do not see the results of any backward rules. Thus layering is still present though you have finer grain control - all your inferences you want the RDFS/OWL rules to see should be forward, all the inferences which need all of the results of the RDFS/OWL rules should be backward. Note that the RDFS and OWL rulesets assume certain settings for the GenericRuleReasoner so a typical configuration is:
Model data = FileManager.get().loadModel("file:data.n3");
List rules = Rule.rulesFromURL("myrules.rules");
GenericRuleReasoner reasoner = new GenericRuleReasoner(rules);
reasoner.setOWLTranslation(true); // not needed in RDFS case
reasoner.setTransitiveClosureCaching(true);
InfModel inf = ModelFactory.createInfModel(reasoner, data);
Where the myrules.rules file will use @include to include one of the RDFS or OWL rule sets.
One useful variant on this option, at least in simple cases, is to manually include a pure (non-hybrid) ruleset for the RDFS/OWL fragment you want so that there is no layering problem. [The reason the default rulesets use the hybrid mode is a performance tradeoff - trying to balance the better performance of forward reasoning with the cost of computing all possible answers when an application might only want a few.]
A simple example of this is that the interesting bits of RDFS can be captured by enabled TranstiveClosureCaching and including just the four core rules:
[rdfs2: (?x ?p ?y), (?p rdfs:domain ?c) -> (?x rdf:type ?c)]
[rdfs3: (?x ?p ?y), (?p rdfs:range ?c) -> (?y rdf:type ?c)]
[rdfs6: (?a ?p ?b), (?p rdfs:subPropertyOf ?q) -> (?a ?q ?b)]
[rdfs9: (?x rdfs:subClassOf ?y), (?a rdf:type ?x) -> (?a rdf:type ?y)]
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2007/10/11 15:01:00
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如何在ontModel上合用owl自带规则和自定义规则
