Uncertainty and Semantic web Jennifer Sleeman Agenda Define uncertainty Provide background Show areas of research Highlight various approaches Provide a demonstration of Pronto Definition - Uncertainty Knowledge can be inaccurate or incomplete Knowledge can be imprecise or “fuzzy” ….leads to uncertainty… Definition - Uncertainty Machine-readable information Applications that work with random information (image processing, geospatial, information retrieval, etc.) Ontology concept definitions Vague concepts: Tall, Small, Big, …. Green, Blue, …. Few, Many, …. Semantic web services ….work with uncertainty… Background – Description Logic Naming Conventions Taken from Wikipedia [12]. Is representing uncertainty necessary? Tim Berner-Lee rejection of uncertainty Not necessary [7] Scalability issues [7] Can you describe knowledge using a “monotonic bivalent language”[7]? What about grey? Uncertainty Is it necessary? Taken from [5] presented at the URSW 2008. General Approaches to Uncertainty and Semantic Web Incomplete/Distorted knowledge [1] • Possibility degrees alternatives Inability to define concepts precisely [1] • Degree of truth Conflicting alternatives [1] • Degree of probability According to [1], since how we solve uncertainty problems depends upon the domain, it is hard to define a single language extension. Areas of Research (based upon 2007/2008 URSW Conference agendas) Extending Semantic Web to support uncertainty Fuzzy theory Probability theory Uncertainty and Ontologies Uncertainty and Web Services Extending the Semantic Web Extend Semantic Web languages to support probabilistic, possibilistic, and fuzzy reasoning Can be at the ontology layer or the rules layer Within the ontology layer proposals for: Syntax and Semantics Logical Formalisms Fuzzy Theory “…In classical set theory, the membership of elements in a set is assessed in binary terms according to a bivalent condition — an element either belongs or does not belong to the set. By contrast, fuzzy set theory permits the gradual assessment of the membership of elements in a set; this is described with the aid of a membership function valued in the real unit interval [0, 1]…”[10] Fuzzy Approaches Extending languages such as OWL with fuzzy extensions Extending Description Logic with fuzzy extensions If a language is extended, one must provide a way to support reasoning of the language with the fuzzy extension Rules and Uncertainty Rules Interchange Format Rules Markup Language For representing/interchanging rules Attempt to provide ways to represent various types of uncertainty [1] Not as much recent attention as ontology layer fuzzy RuleML defines way to specify membership degree [1] Example: Taken from [1]. Fuzzy RDF Extends syntax and semantics of RDF Triple extended to support real number on the interval [0,1] n: s p o [13] Interpretation Subject, object has degree of membership to extension of predicate [13] Satisfies statement if • Membership degree of {subject, object} to the extension of the predicate is >= to n [13] Fuzzy RDF RDFS extended “Class extensions are fuzzy sets of domain elements” [13] Domains are fuzzy and their assignment to properties can also be fuzzy [13] Inference engines can be extended to support such fuzziness Fuzzy Description Logic Fuzzy One such proposal Solve problem of representing and reasoning of fuzzy concepts With concrete domains – reasoning using concrete data types With fuzzy version domains are fuzzy Modifiers are supported (very, slightly, etc.) [12] Fuzzy Description Logic Non-fuzzy Concrete Domain: Concrete Fuzzy Domain: Taken from [12]. Fuzzy Description Logic Interpretations are fuzzy From satisfied/unsatisfied to a degree of truth [0,1] Satisfiability of fuzzy axiom given fuzzy interpretation [12] “Fuzzy axiom a logical consequence of a knowledge base iff every model in the knowledge base satisfies the fuzzy axiom” [12] Reasoning a problem Computationally no calculus exists to check for satisfiability of a fuzzy knowledge model [12] Fuzzy OWL Extension of OWL Example (describing the safety of a location): Without fuzzy, the location is either safe or not safe With fuzzy, the location is safe to a degree Classes and properties are ‘fuzzy’ A class is considered a fuzzy set [1] A property is a fuzzy relation over a set [1] Fuzzy OWL Requires extension of to map OWL entailment to satisfiability [4] Reasoning changes in that when concepts are represented as nodes in forest-like representations, a “membership degree” is associated with each node indicating it belongs to a concept [4] Degrees added to OWL facts Fuzzy OWL Taken from [4]. Probability Theory “..the central objects of probability theory are random variables, stochastic processes, and events: mathematical abstractions of non-deterministic events or measured quantities that may either be single occurrences or evolve over time in an apparently random fashion…” [11] PR-OWL Developed as an extension to OWL (basically an upper ontology) Uses MEBN logic rather than extending OWL Represent conditional probability distribution [21] MFrags organized into MEBN Theories (MTheories) [21] A first order Bayesian logic [21] Consists of entities and attributes Attributes about entities and relationships to each other – MEBN fragments (MFrag) [21] Represents complex Bayesian models [21] Collectively satisfy consistency constraints [21] Goal Provide a way to support Bayesian models PR-OWL Taken from [21]. BayesOWL Express OWL ontologies as Bayesian networks by means of rules For each node, a conditional probability table (CPT) is constructed [15] All subject and object classes translated into concept nodes [15] Arc drawn between 2 concept nodes if the 2 classes are related by predicate [15] Direction based on class hierarchy L-Nodes generated during translation to represent OWL logical operators True/false value for each node indicates whether the instance belongs to the concept CPTs are approximated using the “iterative proportional fitting procedure (IPFP)” [15] Restricted currently to OWL-DL taxonomies [15] Goals Support ontology reasoning using probabilistic approach Support ontology mapping BayesOWL rdfs:subClassOf owl:intersectionOf owl:unionOf owl:complementOf owl:equivalentClass owl:disjointWith Taken from [15]. BayesOWL •DAG constructed •CPTs for LNodes specified •Concept nodes approximated using D-IPFP Taken from [15]. BayesOWL Reasoning Support [15] Concept satisfiability Concept overlapping Concept subsumption Extensions to OWL to support probabilistic representation [15] PriorProb CondProb Concept Mapping [15] BayesOWL Extensions to OWL Taken from [15]. Pronto Non-monotonic probabilistic DL reasoner Built on top of Pellet Uses P-SHIQ(D) formalism [8] Expressing uncertain axioms Probabilistic Reasoning Syntax based upon Lukasiewicz’s conditional constraints [8] Lehmann’s lexicographic entailment [8] Represents uncertain ontological knowledge and reasoning [8] Capable of representing uncertainty in both ABox and TBox axioms [8] “All inferences are done in a totally ‘logical’ way” (no translation) [8] Uses “OWL 1.1 axiom annotations to associate probability intervals with uncertain OWL axioms” [8] Doesn’t scale beyond “15 generic (TBox) conditional constraints” [9] Pronto Conditional constraints (D|C)[l,u] C and D concepts in P-SHIQ(D) [l,u] closed interval within [0,1] Supports overriding Can handle certain probabilistic conflicts Flying birds/penguin problem • Pronto allows “more specific constraints to override more generic ones” [9] • “if Pronto knows that Tweety is a Penguin and Penguin is a subclass-of Bird, it will override the constraint (FlyingObject|Bird)[0.9;1.0] by (FlyingObject|Penguin)[0.0;0.05] and correctly entail Tweety:(FlyingObject|owl:Thing)[0.0;0.05]. “ [9] Uncertainty and Ontologies Mapping Mapping a problem Existing approaches - combination of syntactic and semantic measures [18], use machine learning, or linguistics and natural language processing [15] Quality varies depending upon domain [18] Wang argues without use of a thesaurus, inaccuracies will occur [22] Problem: When mapping a concept from ontology A to ontology B there isn’t always a single concept match but rather a number of concepts that match to some degree Uncertainty and Ontologies Mapping A proposed truth theory solution based on the following [18]: Dempster-Shafer, uncertain reasoning over potential mappings • Evidence Theory Similarity matrix comparing all concepts/properties Similarity measure of a concept between O1 and O2 DS combines evidence learned to form new belief Promising approach Multi-agent ontology mapping framework [18] Not domain dependent Doesn’t require large amounts of training data Uncertainty and Ontologies Mapping A proposed solution by Wang [22]: ACAOM Uses WordNet to calculate similarities for node names Name based mapping Instance strategy • More semantics more feasible to match • Documents assigned to nodes Uses vector space models to rank matches Uncertainty and Ontologies Mapping BayesOWL [15] also proposed a solution Argue that existing similarity approaches will not work • If degree of similarity is not present in both concepts being matched [15] • If concept itself is fuzzy [15] Uses BayesOWL and belief propagation between BNs [15] Ontologies are first translated into BNs [15] Use probabilistic evidence reasoning to determine match [15] Uncertainty and Ontologies – An Ontology of Uncertainty Proposed by the W3C UR3W-XG group Provides a vocabulary for representing different types of uncertainty Was a good start but refinement needed [20] Strategy to use such an ontology as a way to drive a reasoner Open issue: coordination of reasoning of different uncertainty models in knowledge base [19] Uses SWRL rules to assign uncertainty to each relation [19] Uncertainty and Ontologies – An Ontology of Uncertainty Taken from [20]. Uncertainty and Web Services Service discovery – what is best service for request? Matching goal to service Brokers used for filtering Semantic Web Service Framework Semantic Web Service Language – concepts/descriptions [17] Semantic Web Service Ontology – conceptual model [17] It is argued that current frameworks use first order and description logics and “goal capabilities” are “based on subsumption checking or query-answering”[16] Proposed approach uses Incident Calculus [16] Demo - Pronto Pronto Example: Breast Cancer Risk Models Models 2 types of risks – absolute and relative Combining risk factors to determine likelihood of breast cancer for a woman [8] Distinction between known and inferred Pronto uses an ontology for knowledge Uses probabilistic statements to enable computable inferencing [8] The probabilistic statements complement the OWL syntax Demo - Pronto Risk factors relevant to breast cancer are subclasses of ‘RiskFactor’ Categories of women that have certain risk factors are subclasses of ‘WomanWithRiskFactors’ Women with risk of developing cancer subclass ‘WomanUnderBRCRisk’ The goal: “Compute the probability that a certain woman is an instance of some WomanUnderBRCRisk subclass given that she is an instance of some WomanWithRiskFactors subclass” [8] “Infer generic probabilistic subsumption between classes under WomanUnderBRCRisk and under WomanWithRiskFactors” [8] Conditional constraints are used to represent ‘uncertain background knowledge’ using the OWL 1.1 axiom annotations [8] The demo defines constraints to “express how risk factors influence the risk of developing cancer” [8] Pronto combines the factors and computes the probability that a woman is an instance of a subclass of ‘WomanUnderBRCRisk’ Demo - Pronto <owl:ObjectProperty rdf:about="#hasRiskFactor"> <rdfs:domain rdf:resource="#Person"/> <rdfs:range rdf:resource="#RiskFactor"/> </owl:ObjectProperty> <owl:Class rdf:about="#WomanTakingEstrogen"> <owl:equivalentClass> <owl:Restriction> <owl:onProperty rdf:resource="#hasRiskFactor"/> <owl:someValuesFrom rdf:resource="#Estrogen"/> </owl:Restriction> </owl:equivalentClass> <rdfs:subClassOf rdf:resource="#Woman"/> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanWithRiskFactors"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <rdf:Description rdf:about="#Woman"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasRiskFactor"/> <owl:someValuesFrom rdf:resource="#RiskFactor"/> </owl:Restriction> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> <rdfs:subClassOf rdf:resource="#Woman"/> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanAgedUnder50"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <rdf:Description rdf:about="#Woman"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasAge"/> <owl:someValuesFrom rdf:resource="#AgeUnder50"/> </owl:Restriction> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> <rdfs:subClassOf rdf:resource="#WomanWithRiskFactors"/> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanUnderAbsoluteBRCRisk"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <rdf:Description rdf:about="#Woman"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasRisk"/> <owl:someValuesFrom rdf:resource="#AbsoluteBRCRisk"/> </owl:Restriction> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanUnderBRCRisk"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <rdf:Description rdf:about="#Woman"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasRisk"/> <owl:someValuesFrom rdf:resource="#BRCRisk"/> </owl:Restriction> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanUnderIncreasedBRCRisk"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <owl:Restriction> <owl:onProperty rdf:resource="#hasRisk"/> <owl:someValuesFrom rdf:resource="#IncreasedBRCRisk"/> </owl:Restriction> <rdf:Description rdf:about="#WomanUnderBRCRisk"/> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanUnderLifetimeBRCRisk"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <rdf:Description rdf:about="#Woman"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasRisk"/> <owl:someValuesFrom rdf:resource="#LifetimeBRCRisk"/> </owl:Restriction> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> <rdfs:subClassOf rdf:resource="#WomanUnderAbsoluteBRCRisk"/> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanUnderModeratelyIncreasedBRCRisk"> <owl:equivalentClass> <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <rdf:Description rdf:about="#WomanUnderIncreasedBRCRisk"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasRisk"/> <owl:someValuesFrom rdf:resource="#ModeratelyIncreasedBRCRisk"/> </owl:Restriction> </owl:intersectionOf> </owl:Class> </owl:equivalentClass> <rdfs:subClassOf rdf:resource="#WomanUnderIncreasedBRCRisk"/> <owl:disjointWith rdf:resource="#WomanUnderStronglyIncreasedBRCRisk"/> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <owl:Class rdf:about="#WomanUnderModeratelyReducedBRCRisk"> <owl:equivalentClass> <owl:Restriction> <owl:onProperty rdf:resource="#hasRisk"/> <owl:someValuesFrom rdf:resource="#ModeratelyReducedBRCRisk"/> </owl:Restriction> </owl:equivalentClass> <rdfs:subClassOf rdf:resource="#WomanUnderReducedBRCRisk"/> <owl:disjointWith rdf:resource="#WomanUnderStronglyReducedBRCRisk"/> <owl:disjointWith rdf:resource="#WomanUnderWeakelyReducedBRCRisk"/> </owl:Class> Taken from http://clarkparsia.com/pronto/cancer_ra.owl Demo - Pronto <!--Lifetime absolute risk--> <!-- Any woman has a 12.3% risk of lifetime breast cancer --> <owl11:Axiom> <rdf:subject rdf:resource="#Woman"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderLifetimeBRCRisk"/> <pronto:certainty>0;0.123</pronto:certainty> </owl11:Axiom> <!-- If a woman has BRCA mutation, then the risk is beteen 30% and 85% --> <owl11:Axiom> <rdf:subject rdf:resource="#WomanWithBRCAMutation"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderLifetimeBRCRisk"/> <pronto:certainty>0.3;0.85</pronto:certainty> </owl11:Axiom> <!-- If it's BRCA1 mutation, then the lifetime risk is between 60% and 80% --> <owl11:Axiom> <rdf:subject rdf:resource="#WomanWithBRCA1Mutation"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderLifetimeBRCRisk"/> <pronto:certainty>0.6;0.8</pronto:certainty> </owl11:Axiom> Taken from http://clarkparsia.com/pronto/cancer_cc.owl Demo - Pronto <!-- Age-related risk--> <owl11:Axiom> <rdf:subject rdf:resource="#WomanAgedUnder20"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderShortTermBRCRisk"/> <pronto:certainty>0;0.0005</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#WomanAged2030"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderShortTermBRCRisk"/> <pronto:certainty>0;0.004</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#WomanAged3040"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderShortTermBRCRisk"/> <pronto:certainty>0;0.014</pronto:certainty> </owl11:Axiom> Taken from http://clarkparsia.com/pronto/cancer_cc.owl Demo - Pronto <owl11:Axiom> <rdf:subject rdf:resource="#WomanAged4050"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderShortTermBRCRisk"/> <pronto:certainty>0;0.025</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#WomanAged5060"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderShortTermBRCRisk"/> <pronto:certainty>0;0.035</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#WomanAged6070"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderShortTermBRCRisk"/> <pronto:certainty>0;0.039</pronto:certainty> </owl11:Axiom> Taken from http://clarkparsia.com/pronto/cancer_cc.owl Demo - Pronto <!--owl11:Axiom> <rdf:subject rdf:resource="#Julie"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#WomanAged3040"/> <pronto:certainty>1;1</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#Mary"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#WomanWithBRCA1Mutation"/> <pronto:certainty>1;1</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#Ann"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#WomanWithMotherBRCAffected"/> <pronto:certainty>1;1</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#Ann"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#AshkenaziJewishWoman"/> <pronto:certainty>0.9;0.95</pronto:certainty> </owl11:Axiom--> Taken from http://clarkparsia.com/pronto/cancer_cc.owl Demo - Pronto <owl11:Axiom> <rdf:subject rdf:resource="#Helen"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#PostmenopausalWoman"/> <pronto:certainty>1;1</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#Helen"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#WomanTakingEstrogen"/> <pronto:certainty>1;1</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#Helen"/> <rdf:predicate rdf:resource="&rdf;type"/> <rdf:object rdf:resource="#WomanTakingProgestin"/> <pronto:certainty>1;1</pronto:certainty> </owl11:Axiom> Taken from http://clarkparsia.com/pronto/cancer_cc.owl Demo - Pronto <owl11:Axiom> <rdf:subject rdf:resource="#AshkenaziJewishWoman"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanWithBRCAMutation"/> <pronto:certainty>0.025;0.025</pronto:certainty> </owl11:Axiom> <owl11:Axiom> <rdf:subject rdf:resource="#WomanWithBRCAMutation"/> <rdf:predicate rdf:resource="&rdfs;subClassOf"/> <rdf:object rdf:resource="#WomanUnderLifetimeBRCRisk"/> <pronto:certainty>0.3;0.85</pronto:certainty> </owl11:Axiom> Demo - Pronto Running query (generic TBox conditional constraint) (C|D)[l,u] [9] entail http://clarkparsia.com/pronto/cancer_ra.ow l#AshkenaziJewishWoman http://clarkparsia.com/pronto/cancer_ra.ow l#WomanUnderLifetimeBRCRisk Demo - Pronto Query : entail Result: 34: (WomanUnderLifetimeBRCRisk|AshkenaziJewishWoman)[0.0075;0.123] Explanation: Explaining the generic constraint 34: (WomanUnderLifetimeBRCRisk|AshkenaziJewish Woman)[0.0075;0.123]: Lower bound is because of: [[8: (WomanWithBRCAMutation|AshkenaziJewishWoman)[0.025;0.025], 7: (WomanUnderLi fetimeBRCRisk|WomanWithBRCAMutation)[0.3;0.85]]] Upper bound is because of: [[10: (WomanUnderLifetimeBRCRisk|Woman)[0.0;0.123]]] Result computed in 6266ms Want to learn more? Attend the 2009 URSW Conference Visit W3C Uncertainty Reasoning for the World Wide Web Incubator Group http://c4i.gmu.edu/ursw/2008/ Download Pronto http://www.w3.org/2005/Incubator/urw3/ Review presentations from last year’s conference http://c4i.gmu.edu/ursw/2009/ http://pellet.owldl.com/pronto/ Download FiRE http://www.image.ece.ntua.gr/~nsimou/FiRE/ References [1] - Stoilos,Simou,Stamou,Kollias,“Uncertainty and the Semantic Web”, http://www.image.ece.ntua.gr/php/savepaper.php?id=445, 2006, IEEE [2] – 2008 Conference, “Uncertainty Reasoning for the Semantic Web”, http://c4i.gmu.edu/ursw/2008/index.html [3] - 2007 Conference, “Uncertainty Reasoning for the Semantic Web”, http://c4i.gmu.edu/ursw/2007/index.html [4] - Stoilos,Stamou,Tzouvaras,Pan,Horrocks, “Fuzzy OWL: Uncertainty and the Semantic Web”, http://www.image.ntua.gr/papers/398.pdf [5] - Lassila, “Some Personal Thoughts on Semantic Web and “Non-symbolic” AI”, http://c4i.gmu.edu/ursw/2008/talks/URSW2008_Keynote_Lassila.pdf, 2008, ISWC [6] – Williams,Bastin,Cornford,Ingram, “Describing and Communicating Uncertainty within the Semantic Web”, http://c4i.gmu.edu/ursw/2008/papers/URSW2008_F3_WilliamsEtAl.pdf [7] – Sanchez, “Fuzzy logic and semantic web”, http://books.google.com/books?id=Cidej8b4ESIC&pg=PA4&lpg=PA4&dq=monotonic+bivalent+language&source=bl&ots=mtbZcZfaO7&sig=VtGqKXurrzl5HOw36UBTeTpdoE&hl=en&ei=sBIASpuJFonItgeKnpyTBw&sa=X&oi=book_result&ct=result&resnum=1#PPP1,M1 [8] – Klinov, Parsia, “Demonstrating Pronto: a Non-monotonic Probabilistic OWL Reasoner”, http://www.webont.org/owled/2008dc/papers/owled2008dc_paper_2.pdf [9] – Klinov, “Introducing Pronto: Probabilistic DL Reasoning in Pellet“, http://clarkparsia.com/weblog/2007/09/27/introducing-pronto/ [10] – Wikipedia Fuzzy Set theory, http://en.wikipedia.org/wiki/Fuzzy_set [11] – Wikipedia Probability Theory, http://en.wikipedia.org/wiki/Probability_theory [12] – Straccia, “A Fuzzy Description Logic for the Semantic Web”, http://www.win.tue.nl/~aserebre/ks/Lit/Straccia2006.pdf [13] – Mazzieri, Dragoni, “A Fuzzy Semantics for Semantic Web Languages”, http://ftp.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-173/paper2.pdf [14] – Wikipedia Description Logic, http://en.wikipedia.org/wiki/Description_logic [15] – Ding, Peng, Pan, “BayesOWL: Uncertainty Modeling in Semantic Web Ontologies”, http://ebiquity.umbc.edu/_file_directory_/papers/217.pdf [16] – Martin-recurerda1, Robertson2, “Discovery and Uncertainty in Semantic Web Services”, http://ftp.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol173/paper4.pdf [17] – “Semantic Web Services Framework (SWSF) Overview”, http://www.w3.org/Submission/SWSF/ [18] – Nagy,Vargas-Vera,Motta, “Uncertain Reasoning for Creating Ontology Mapping on the Semantic Web”, http://c4i.gmu.edu/ursw/2007/files/papers/URSW2007_P2_NagyVeraMotta.pdf [19] – Ceravolo, Damiani,Leida, “Which Role for an Ontology of Uncertainty?”, http://c4i.gmu.edu/ursw/2008/papers/URSW2008_P6_CeravoloEtAl.pdf [20] – Laskey, Laskey, “Uncertainty Reasoning for the World Wide Web: Report on the URW3-XG Incubator Group”, http://c4i.gmu.edu/ursw/2008/papers/URSW2008_FX_LaskeyLaskey.pdf [21] – Costa, Laskey, “PR-OWL: A Framework for Probabilistic Ontologies”, http://volgenau.gmu.edu/~klaskey/papers/FOIS2006_CostaLaskey.pdf [22] – Wang, “Integrating Uncertainty Into Ontology Mapping”, http://iswc2007.semanticweb.org/papers/955.pdf