From SHIQ and RDF to OWL: The Making of a Web Ontology Language
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1 From SHIQ and RDF to OWL: The Making of a Web Ontology Language Ian Horrocks Peter F. Patel-Schneider and Frank van HarmelenPresented by Zonghui Lian
2 Ontology Languages So far, how many ontology languages we can know XOL (XML-based Ontology Exchange Language)SHOE (Simple HTML Ontology Extension)OML (Ontology Markup Language)RDF(S) (Resource Description Framework (Schema))OIL (Ontology Interchange Language)DAML+OIL (DARPA Agent Markup Language + OIL)OWL (Ontology Web Language)
3 XML – XML SchemaXML provides a standardized syntactical way to expose structural informationXML schema allows to define a schema for XML documents and may already provide machine-understandable semantics of dataDo not attach meaning to structural information
4 RDF Schema RDFS is too weak to describe resources in sufficient detail No localised range and domain constraintsFor example, can’t express such a subclass of person: the person who has children.No existence/cardinality constraintsCan’t say that all instances of person have a mother that is also a person, or that persons have exactly 2 parentsNo transitive, inverse or symmetrical propertiesCan’t say that isPartOf is a transitive property, that hasPart is the inverse of isPartOf or that touches is symmetricalDifficult to provide reasoning supportRDF has fact-stating ability.Symmetric: if P(x, y) then P(y, x)Transitive: if P(x,y) and P(y,z) then P(x, z)Functional: if P(x,y) and P(x,z) then y=zInverseOf: if P1(x,y) then P2(y,x)InverseFunctional: if P(y,x) and P(z,x) then y=zallValuesFrom: P(x,y) and y=allValuesFrom(C)someValuesFrom: P(x,y) and y=someValuesFrom(C)hasValue: P(x,y) and y=hasValue(v)cardinality: cardinality(P) = NminCardinality: minCardinality(P) = NmaxCardinality: maxCardinality(P) = NequivalentProperty: P1 = P2intersectionOf: C = intersectionOf(C1, C2, …)unionOf: C = unionOf(C1, C2, …)complementOf: C = complementOf(C1)oneOf: C = one of(v1, v2, …)equivalentClass: C1 = C2disjointWith: C1 != C2sameIndividualAs: I1 = I2differentFrom: I1 != I2AllDifferent: I1 != I2, I1 != I3, I2 != I3, …Thing: I1, I2, …Legend:Properties are indicated by: P, P1, P2, etcSpecific classes are indicated by: x, y, zGeneric classes are indicated by: C, C1, C2Values are indicated by: v, v1, v2Instance documents are indicated by: I1, I2, I3, etc.A number is indicated by: NP(x,y) is read as: “property P relates x to y”
5 RequirementsDesirable features identified for a Web Ontology Language :Compatible with existing Web standards (XML, RDF, RDFS)Easy to understand and useFormally specifiedHas “adequate” expressive powerTools for reasoning support
6 Layers of Languages Attribution Explanation We are here! IdentityStandard SyntaxMetadataOntologiesRules & InferenceExplanationAttributionComplexity could be a problem
7 OWL (Ontology Web Language) OWL is now a W3C RecommendationThe purpose of OWL is identical to RDFS i.e. to provide an XML vocabulary to define classes, properties and their relationships.RDFS enables us to express basic relationships and has limited inferencing capability.OWL enables us to express much richer relationships, thus yielding a much enhanced inferencing capability.The benefit of OWL is that it facilitates a much greater degree of inferencing than you get with RDF Schema.
9 Introduction of OWL (Ontology Web Language) Description logic and framesMany characteristics of RDFThe frame includes the name of the class, identifies the more general class (or classes) that it specialises, and lists a set of “slots”. A slot may consist of a property-valuepair, or a constraint on the values that can act as slot “fillers” (in this context, value means either an individual or a data value). This structure was used in the OIL language, with some enrichment of the syntax for specifying classes and slot constraints so as to enable the full power of a Description Logic style language to be captured.
10 D.L’s Influence on OWL Semantics are well defined. OWL uses D.L model theory to formalise the meaning of the language.AdvantagesReasoning technique --- check the consistency of classes and ontologies, and to check entailment relationships. Assume a query …
11 D.L’s Influence on OWL Language constructors Expressive power Class (property) constructorsAxiomsConflict with the computational complexityOWL entailmentBlanceBoolean connectives, restriction on properties, transtive properties, and property hierarchy
12 D.L’s Influence on OWL Datatypes Difference with Advantage Decrease the complexity & easy to answer question“-5 nonNegative ?”Totally seperated, 2nd indicates abstract concepts.
13 Origins of OWL DARPA Agent Markup Language DAML Ontology Inference LayerOILRDFEU/NSF Joint Ad hoc CommitteeDAML+OILAll influenced by RDFOil: the precise details of RDF semantics.OWL provides the complex inferences, undecidable.OWL LiteOWL DLOWL FullA W3CRecommendationOWL
14 Versions of OWLDepending on the intended usage, OWL provides three increasingly expressive sublanguagesOWL FullFull: Consider the compatibility with RDF and RDFS as the primary importance. no computation guaranteesDL (Description Logic): Friendly syntax, decidable inference. computationally completeLite: Simpler syntax and more tractable inference.OWL DLOWL Lite
15 Advantages/Disadvantages of versions Full:The advantage of the Full version of OWL is that we get the full power of the OWL language.The disadvantage is that it is very difficult to build a computational tool for this version and may not get a quick and complete answer.DL/Lite:The advantage of the DL or Lite version of OWL is that tools can be built more quickly and easily, and users can expect responses from such tools to come quicker and be more complete.The disadvantage is that we don't have access to the full power of the language.