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Semantic Web Ontologies & Data Models

Semantic Web Ontologies & Data Models. CS 502 – 20020307 Carl Lagoze – Cornell University. Acknowledgements: Eric Miller Dieter Fensel. Components of the Semantic Web. What is an Ontology ?. A formal specification of conceptualization shared in a community

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Semantic Web Ontologies & Data Models

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  1. Semantic WebOntologies & Data Models CS 502 – 20020307 Carl Lagoze – Cornell University Acknowledgements: Eric Miller Dieter Fensel 20020307

  2. Components of the Semantic Web 20020307

  3. What is an Ontology? • A formal specification of conceptualization shared in a community • Vocabulary for defining a set of things that exist in a world view • Formalization allows communication across application systems and extension • Parallel concepts in other areas: • Domains: database theory • Types: AI • Classes: OO systems • Types/Sorts: Logic • Global vs. Domain-specific 20020307

  4. XML and RDF are ontologically neutral • No standard vocabulary just primitives • Resource, Class, Property, Statement, etc. • Compare to classic first order logic • Conjunction, disjunction, implication, existential, universal quantifier 20020307

  5. Components of an Ontology • Vocabulary (concepts) • Structure (attributes of concepts and hierarchy) • Logical characteristics of concepts & attributes • Domain and range restrictions • Properties of relations (symmetry, transitivity) 20020307

  6. Wordnet • On-line lexical reference system, domain-independent • >100,000 word meanings organized in a taxonomy with semantic relationships • Synonymy, meronymy, hyponymy, hypernymy • Useful for text retrieval, etc. • http://www.cogsci.princeton.edu/~wn/online/ 20020307

  7. CYC • Effort in AI community to accommodate all of human knowledge!!! • Formalizes concepts with logical axioms specifying constraints on objects and classes • Associated reasoning tools • Contents are proprietary but there is OpenCyc • http://www.opencyc.org/ 20020307

  8. Ontologies for the Web • Lots of Participants and $$$ • Web Ontology Working Group • Distributed Agent Markup Language • Ontology Inference Layer • OntoWeb • Schemas Project • DAML+OIL – develop standard for encoding ontologies on top of RDF Schema 20020307

  9. Extending RDF(S) with DAML+OIL RDFS DAML+OIL • Class definition: Conjunction, disjunction, negation • Property constraints: universality, existence, cardinality • Properties of properties: transitivity, symmetry • Class, sub-class definition • Property (attribute), sub-property definition • Domain, range constraints 20020307

  10. DAML class building operations • disjointWith • No vegetarians are carnivores • sameClassAs (equivalence) • Enumerations (on instances) • The Ivy League is Cornell, Harvard, Yale, …. • Boolean set semantics (on classes) • Union (logical disjunction) • Intersection (logical conjunction) • complimentOf (logical negation) • All non-carnivores are vegetarians 20020307

  11. DAML property building operations & restrictions • Unique Property: subject identifies object • Unambiguous Property: object identifiers subject • Inverse of • hasChild is inverse of hasParent • Transitivity (e.g., descendent relationship) • Cardinality (exact, max, min) 20020307

  12. DAML+OIL DataTypes • Full use of XML schema data type definitions • Examples • Define a type age that must be a non-negative integer • Define a type clothing size that is an enumeration “small” “medium” “large” 20020307

  13. DAML+OIL Instance Creation • Create individual objects filling in slot/attribute/property definitions <Person ref:ID=“William Arms”> <rdfs:label>Bill</rdfs:label> <age><xsd:integer rdf:value=“55”/></age> <shoesize><xsd:decimal rdf:value=“10.5”/></shoesize></Person> 20020307

  14. Language Comparison 20020307

  15. Some useful RDF tools • JENA toolkit for manipulating RDF models • http://www.hpl.hp.com/semweb/jena-top.html • RDFSviz for visualizing ontologies expressed as RDF schema • http://www.dfki.uni-kl.de/frodo/RDFSViz/ • W3C RDF validation service for parsing and view RDF instances • http://www.w3.org/RDF/Validator/ 20020307

  16. But modeling the way things “are” is not always enough ABC – Modeling how things (or their descriptions) change 20020307

  17. ABC Example Leo Tolstoy, who was born in Moscow in 1828, authored a manuscript called “War and Peace” in 1855. In 1860, that manuscript as the book “Illustrated War and Peace”, was published by Russia Publishers, with Tolstoy supplying the illustrations. 20020307

  18. ABC Model Overview • (Digital) objects have inherent lifecycle characteristics • Model creation, evolution, and transformation of objects over time. • Notions of temporality are given first-class status • Measuring utility of metadata through query-ability • Ability to answer who, what, when, where comments that are difficult in simpler models • Descriptions provide a world context • From ambiguous to exact information – only say what you know 20020307

  19. Entities and their Properties • Entities are anchor points for set of properties • Entities "change" by modification of property sets • Model does not distinguish between "change of nature" and "change of description" • Dual facets of Entities • Universal – object and its property set that is "global" to the description • Existential – object instances and their property sets that are periodic ("stateful") 20020307

  20. Situations • Establish a time period • granularity determined by the longevity of entity state within situation • Situations and actualities • Situations provide context for associating entities in their existential facet. • Entities can exist out of situation to express their universal properties 20020307

  21. Events • Transition marker point between situations • Always have a time property • Levels of increasing knowledge • Something happened at a time (that caused change in situation) • Type thing happened at some time • Anchor point for multiple actions (verbs) within a happening. 20020307

  22. Events, Actions, Agents • Events provide a context for associating actions ("verbs"), 1-n • Actions provide a context for participation of agents, 1-n • Participation type can be specialized for domain 20020307

  23. Causality – verbs & predicates • Association of actions to Actualities in preceding situation is weak • Increasing knowledge of association (esp. important in rights management) • involves • hasTool • hasPatient 20020307

  24. Intellectual Property • Notion of "ability to copy" is the determining factor • Promote abstraction to work and actuality to manifestation and item 20020307

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