1 Inference rules for RDF(S) and OWL in N3Logic Dominik Tomaszuk Institute of Computer Science University of Bialystok Poland Email: [email protected] Abstract—This paper presents inference rules for Resource infinite)setofblanknodes,Lthesetofliterals.AnRDFtriple Description Framework (RDF), RDF Schema (RDFS) and Web t is defined as a triple t=(cid:104)s,p,o(cid:105) where s∈I∪B is called Ontology Language (OWL). Our formalization is based on 6 the subject, p ∈ I is called the predicate and o ∈ I ∪B∪L Notation 3 Logic, which extended RDF by logical symbols and 1 is called the object. createdSemanticWeblogicfordeductiveRDFgraphstores.We 0 alsoproposeOWL-PthatisalightweightformalismofOWLand 2 TheelementalconstituentsoftheRDFdatamodelareRDF supportssoftinferencesbyomittingcomplexlanguageconstructs. termsthatcanbeusedinreferencetoresources:anythingwith n a identity. The set of RDF terms is divided into three disjoint J subsets: IRIs, literals, and blank nodes. 1 I. INTRODUCTION Definition 2 (IRIs). IRIs serve as global identifiers that can 1 Resource Description Framework (RDF) is a general be used to identify any resource. ] methodforconceptualdescriptionormodelingofinformation B that is implemented in web resources. RDF Schema (RDFS) Definition 3 (Literals). Literals are a set of lexical values. It D extends RDF to classes providing basic elements for the can be a set of plain strings, such as "Apple", optionally with an associated language tag, such as "Apple"@en. . description of vocabularies. OWL adds more vocabulary for s c describingpropertiesandclassesi.e.relationsbetweenclasses, Remark 1. In RDF 1.1 literals comprise [ cardinality, and richer typing of properties. Unfortunately, a lexical string and a datatype, such as 1 OWLhashighworst-casecomplexityresultsforkeyinference "1"ˆˆhttp://www.w3.org/2001/XMLSchema#int. v problems.Toovercomethisproblemweproposealightweight 0 OWL profile called OWL-P. Remark 2. In literals datatypes are identified by IRIs, where 5 A rule is perhaps one of the most understandable notion RDF borrows many of the datatypes defined in XML Schema 6 in computer science. It consists of the condition and the 1.1 [26]. 2 conclusion.Ifsomeconditionthatischeckableinsomedataset 0 Definition 4 (Blank nodes). Blank nodes are defined as 1. holds, then the conclusion is processed. In the same way existential variables used to denote the existence of some RDF(S) and OWL entailments work. 0 resource for which an IRI or literal is not given. 6 The paper is constructed according to sections. Section II 1 presentsRDFandNotation3Logicconcepts.InSectionIIIwe Remark 3. Blank nodes are inconstant or stable identifiers : presentinferencerulesforRDF.RDFSandOWLinN3Logic. and are in all cases locally scoped to the RDF store or the v i Section IV is devoted to related work. The paper ends with RDF file. X conclusions. AcollectionofRDFtriplesintrinsicallyrepresentsalabeled r a directedmultigraph.Thenodesarethesubjectsandobjectsof II. PRELIMINARIES theirtriples.RDFisoftenreferredtoasbeinggraphstructured The RDF data model rests on the concept of creating web- data where each (cid:104)s,p,o(cid:105) triple can be interpreted as an edge p resource statements in the form of subject-predicate-object s−→o. expressions, which in the RDF terminology, are referred to Definition5(RDFgraph). LetO =I∪B∪LandS =I∪B, as triples (or statements). then G⊂S×I×O is a finite subset of RDF triples, which An RDF triple comprises a subject, a predicate, and an is called RDF graph. object.In[28],themeaningofsubject,predicateandobjectis explained. The subject denotes a resource, the object fills the On the other hand, in the Semantic Web environment value of the relation, the predicate refers to the resource’s there is a Notation3 format, which offers a new human- characteristics or aspects and expresses a subject – object readableserializationofRDFmodelbutitalsoextendedRDF relationship. The predicate denotes a binary relation, also by logical symbols and created a new Semantic Web logic known as a property. called Notation3 Logic (N3Logic). Following [2], we provide Following[28],weprovidedefinitionsofRDFtriplesbelow. definitions of N3Logic below. Definition 1 (RDF triple). Assume that I is the set of all Definition 6 (N3Logic alphabet). A N3Logic alphabet A N3 Internationalized Resource Identifier (IRI) references, B (an consists of the following disjoint classes of symbols: 2 TABLEIII 1) asetI ofIRIsymbolsbeginningwith<andendingwith VOCABULARYTERMSUSEDINLODSNAPSHOT2015 >, 2) a set L of literals beginning and ending with ", vocterms owl:AllDifferent 111 3) a set V of variables, V = B∪V , where B is a set of U owl:AllDisjointClasses 21 existential variables (blank nodes in RDF-sense) start owl:AllDisjointProperties 13 with _: and V is a set of universal variables start owl:allValuesFrom 126330 U owl:assertionProperty 0 with ?, owl:AsymmetricProperty 0 4) brackets {, }, owl:cardinality 23910 5) a logical implication =>, owl:complementOf 873 owl:DatatypeProperty 27471 6) a period ., owl:differentFrom 784 7) a period @false. owl:disjointUnionOf 0 owl:disjointWith 3743 Remark 4. Notation3 allows to abbreviate IRIs by using owl:equivalentClass 29708 prefixes. Instead of writing <http://example.com>, we owl:equivalentProperty 201 owl:FunctionalProperty 3730 can write ex:. owl:hasKey 5 owl:hasSelf 3 Remark 5. Each IRI, variable and literal is an expression. owl:hasValue 1877 owl:intersectionOf 2681 Remark 6. {f} is an expression called formula. owl:InverseFunctionalProperty 94 owl:inverseOf 1341 Remark 7. e1 => e2 is a formula called implication. owl:IrreflexiveProperty 0 owl:maxCardinality 257371 InNotation3literals,IRIs,variablesorevenformulaexpres- owl:minCardinality 455203 sions can be subjects, objects or predicates. owl:ObjectProperty 40330 owl:oneOf 853 owl:propertyChainAxiom 68 owl:propertyDisjointWith 4 III. INFERENCERULES owl:qualifiedCardinality 109 owl:qualifiedMaxCardinality 2 Inthissection,weintroduceinferencerulesforRDF,RDFS owl:qualifiedMinCardinality 20 and OWL. Inference rules connected with RDF(S) and OWL owl:sameAs 3967150 owl:someValuesFrom 4446 are basis of the deductive RDF graph stores. owl:sourceIndiviual 0 owl:SymmetricProperty 194 Definition 7 (Deductive RDF graph store). A deductive RDF owl:targetIndividual 0 graphstoreisanentitywhichremembersRDFtriplesandcan owl:targetValue 11 generatenewonesundercertainconditionsthroughdeduction owl:TransitiveProperty 267 owl:unionOf 53735 or inference. It can answer queries about the combined given rdfs:domain 111865 and inferred triples. rdfs:range 59252 rdfs:subClassOf 1339391 rdfs:subPropertyOf 13416 A. RDF and RDFS In Table I we present patterns which hold by RDF and IV. RELATEDWORK RDFS entailments. All rules are tested in reasoning engines One of the most important general purpose logic program- such as FuXi1 and cwm2. minglanguageisProlog[4].Itisdeclarative,whichmeansthat theprogramlogicisdeclaredintermsofrelations,represented as facts and rules. Yet anoder declarative language is Datalog B. OWL [5], which is syntactically a subset of Prolog. Apart from the In Table II we analyze existing proposals for different Notation3,thereareotherrule-basedinferenceenginesformats OWL2 profiles: RDFS++ [1], L2 [6], RDF 3.0/OWLPrime fortheSemanticWeb,suchas:FOL-RuleML[8],SWRL[12], [10], OWLSIF/pD* [27], OWL-LD [7] and OWL-RL [20]. RIF [14], R-DEVICE [3], TRIPLE [25], Jena rule3 and SPIN We check which terms are most commonly used and propose [17]. a new version of OWL 2 called OWL-P. We also considered FOL-RuleML (First-order Logic Rule Markup Language) time complexity for detecting a required rule application and [8] is a rule language for expressing first-order logic for the frequently used vocabulary terms in our corpus. The snapshot web.ItisasublanguageofRuleML[9].InFOL-RuleMLeach (Table III) is built by [13] and use seeds from [24]. of rules consists of a set of statements called an atom. The This profile of OWL2 is simpler that OWL-RL. It drops atomisaformwhichconsistsofobjectswhichareindividuals support for restriction and cardinality classes, class relation- or variables, and a relation between them. ships and list-based axioms. In the Table IV, Table V and we SWRL (Semantic Web Rule Language) [12] is based on present inference rules of OWL-P. OWL [21] and Unary/Binary Datalog RuleML, which sublan- guage of the RuleML. It extends the set of OWL axioms to 1https://github.com/RDFLib/FuXi 2http://www.w3.org/2000/10/swap/doc/cwm.html 3http://jena.apache.org/documentation/inference 3 TABLEI INFERENCERULESFORRDFANDRDFS Conditions Conclusions {?S ?P ?O} => {?P rdf:type rdf:Property}. {?P rdfs:domain ?C. ?S ?P ?O} => {?S rdf:type ?C}. {?P rdfs:range ?C. ?S ?P ?O} => {?O rdf:type ?C}. {?S ?P ?O} => {?S rdf:type rdfs:Resource}. {?S ?P ?O} => {?O rdf:type rdfs:Resource}. {?Q rdfs:subPropertyOf ?R. ?P rdfs:subPropertyOf ?Q} => {?P rdfs:subPropertyOf ?R}. {?Q rdf:type rdf:Property} => {?Q rdfs:subPropertyOf ?Q}. {?P rdfs:subPropertyOf ?R. ?S ?P ?O} => {?S ?R ?O}. {?C rdf:type rdfs:Class} => {?C rdfs:subClassOf rdfs:Resource}. {?A rdfs:subClassOf ?B. ?S rdf:type ?A} => {?S rdf:type ?B}. {?Q rdf:type rdfs:Class} => {?Q rdfs:subClassOf ?Q}. {?B rdfs:subClassOf ?C. ?A rdfs:subClassOf ?B} => {?A rdfs:subClassOf ?C}. {?X rdf:type rdfs:ContainerMembershipProperty} => {?X rdfs:subPropertyOf rdfs:member}. {?X rdf:type rdfs:Datatype} => {?X rdfs:subClassOf rdfs:Literal}. TABLEII COMPARISONOFOWLPROFILES OWL-P RDFS++ L2 RDFS3.0 OWLSIF OWL-LD OWL-RL OWLPrime pD* owl:AllDifferent owl:AllDisjointClasses (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) owl:AllDisjointProperties (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:allValuesFrom (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:assertionProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) owl:AsymmetricProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:cardinality (cid:50)(cid:8) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) owl:complementOf (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:DatatypeProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) owl:differentFrom (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) owl:disjointUnionof (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:disjointWith (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:equivalentClass (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:equivalentProperty (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:FunctionalProperty (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:hasKey (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:hasSelf (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:hasValue (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:intersectionof (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) owl:InverseFunctionalProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:inverseOf (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:IrreflexiveProperty (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:maxCardinality (cid:50)(cid:8) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) owl:minCardinality (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:ObjectProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:oneOf (cid:50)(cid:8) (cid:52) (cid:52) (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) owl:propertyChainAxiom (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:propertyDisjointWith (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:qualifiedCardinality (cid:50)(cid:8) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) owl:qualifiedMaxCardinality (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:qualifiedMinCardinality (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:sameAs (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:someValuesFrom (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:sourceIndiviual (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) owl:SymmetricProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:targetIndividual (cid:50)(cid:8) (cid:52) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) owl:targetValue (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:TransitiveProperty (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) owl:unionof (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) rdfs:domain (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:52) (cid:50)(cid:8) rdfs:range (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) rdfs:subClassOf (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) rdfs:subPropertyOf (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) (cid:50)(cid:8) 4 TABLEIV INFERENCERULESFOROWL-PPROPERTIES Conditions Conclusions {?S ?P ?O} => {?S owl:sameAs ?S. ?P owl:sameAs ?P. ?O owl:sameAs ?O}. {?S owl:sameAs ?O} => {?O owl:sameAs ?S}. {?Q owl:sameAs ?R. ?R owl:sameAs ?P} => {?Q owl:sameAs ?P}. {?S owl:sameAs ?S2. ?S ?P ?O} => {?S2 ?P ?O}. {?P owl:sameAs ?P2. ?S ?P ?O} => {?S ?P2 ?O}. {?O owl:sameAs ?O2. ?S ?P ?O} => {?S ?P ?O2}. {?Q owl:sameAs ?R. ?Q owl:differentFrom ?R} => {@false}. {?P rdf:type owl:FunctionalProperty. ?Q ?P ?R1. ?Q ?P ?R2} => {?R1 owl:sameAs ?R2}. {?P rdf:type owl:InverseFunctionalProperty. ?Q1 ?P ?R. ?Q2 ?P ?R} => {?Q1 owl:sameAs ?Q2}. {?P rdf:type owl:IrreflexiveProperty. ?Q ?P ?Q} => {@false}. {?P rdf:type owl:SymmetricProperty. ?Q ?P ?R} => {?R ?P ?Q}. {?P rdf:type owl:AsymmetricProperty. ?Q ?P ?R. ?R ?P ?Q } => {@false}. {?P rdf:type owl:TransitiveProperty. ?Q ?P ?R. ?R ?P ?P} => {?Q ?P ?P}. {?P1 owl:equivalentProperty ?P2. ?Q ?P1 ?R} => {?Q ?P2 ?R}. {?P1 owl:equivalentProperty ?P2. ?Q ?P2 ?R} => {?Q ?P1 ?R}. {?P1 owl:propertyDisjointWith ?P2. ?Q ?P1 ?R. ?Q ?P2 ?R} => {@false}. {?P1 owl:inverseOf ?P2. ?Q ?P1 ?R} => {?R ?P2 ?Q}. {?P1 owl:inverseOf ?P2 . ?Q ?P2 ?R} => {?R ?P1 ?Q}. TABLEV INFERENCERULESFOROWL-PCLASSES Conditions Conclusions {?A owl:equivalentClass ?B . ?x rdf:type ?A} => {?x a ?B}. {?A owl:equivalentClass ?B . ?x rdf:type ?B} => {?x a ?A}. {?A owl:disjointWith ?B. { ?x rdf:type ?A. ?x rdf:type ?B} => {@false} {?C rdf:type owl:Class} => {?C rdfs:subClassOf ?C. ?C owl:Thing. ?C owl:equivalentClass ?C. owl:Nothing rdfs:subClassOf ?C}. {?A owl:equivalentClass ?B} => {?A rdfs:subClassOf ?B. ?B rdfs:subClassOf ?A}. {?A rdfs:subClassOf ?B. ?B rdfs:subClassOf ?A} => {?A owl:equivalentClass ?B}. {?P rdf:type owl:ObjectProperty} => {?P rdfs:subPropertyOf ?P. ?P owl:equivalentProperty ?P}. {?P rdf:type owl:DatatypeProperty} => {?P rdfs:subPropertyOf ?P. ?P owl:equivalentProperty ?P}. {?P owl:equivalentProperty ?R} => {?P rdfs:subPropertyOf ?R. ?R rdfs:subPropertyOf ?P}. {?P rdfs:subPropertyOf ?R. ?R rdfs:subPropertyOf ?P} => {?P owl:equivalentProperty ?R}. include Horn-like rules. Logical operators and quantifications supportsasecond-ordersyntax,wherevariablescanrangeover supports of SWRL are the same as in RuleML. Moreover, classes and properties. It provides a RuleML-like syntax. RuleMLcontentscanbepartsofSWRLcontent.Axiomsmay TRIPLE [25] is an RDF rule (query, inference, and trans- consist of OWL, RDF and rule axioms. A relation can be an formation) language, with a layered and modular nature. It is IRI, a data range, an OWL property or a built-in relation. An basedonHornLogic[11]andF-Logic[16].RulesinTRIPLE object can be a variable, an individual, a literal value or a areusedfortransientqueryingandcannotbeusedfordefining blank node. and maintaining views. RIF (Rule Interchange Format) [14] is a standard for SPIN (SPARQL Inferencing Notation) [17] is a constraint exchanging rules among disparate systems. It focused on and SPARQL-based rule language for RDF. It can link class exchange rather than developing a single one-fits-all rule withqueriestocaptureconstraintsandruleswhichdescribethe language. It can be separated into a number of parts, RIF- behavior of those classes. SPIN is also a method to represent core [23] which is the common core of all RIF dialects, queries as templates. It can represent SPARQL statement as RIF-BLD(BasicLogicDialect)[15]comprisingbasicdialects RDF triples. That proposal allows to declare new SPARQL (i.e. Horn rules) for writing rules, RIF-PRD [18] (Production functions. Rule Dialect) for representing production rules and RIF-DTB Jena rule is a rule format used only by inference engine in (Datatypes and Built-in Functions) [22] comprising a set of the Jena framework [19]. The rule language syntax is based datatypes and built-in functions. on RDF. It uses the triple representation, which is similar to R-DEVICE [3] is a deductive rule language for reasoning Notation3 except that a rule name can be specified in a rule. about RDF data. In R-DEVICE resources are represented There are not any formula notation, and built-in functions are as objects and RDF properties are realized as multi-slots. It written in function terms. 5 V. CONCLUSIONS [21] Bijan Parsia, Sebastian Rudolph, Markus Kro¨tzsch, Peter Patel- Schneider, and Pascal Hitzler. OWL 2 Web Ontology Language This paper define how knowledge and logic might be han- Primer (Second Edition). W3C recommendation, World Wide Web dled on the Semantic Web environment. We present inference Consortium, December 2012. http://www.w3.org/TR/2012/REC-owl2- rules RDF, RDF Schema and OWL. All rules are tested in primer-20121211/. [22] Axel Polleres, Michael Kifer, and Harold Boley. RIF Datatypes and reasoning engines. Our formalization is based on Notation 3 Built-Ins 1.0 (Second Edition). 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