Semantic Web Ontologies Data Models CS 502 20020307 Carl Lagoze Cornell University Acknowledgements Eric Miller Dieter Fensel Cornell CS 502 20020307 Components of the Semantic Web Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 Wordnet On line lexical reference system domainindependent 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 Extending RDF S with DAML OIL RDFS Class sub class definition Property attribute sub property definition Domain range constraints Cornell CS 502 DAML OIL Class definition Conjunction disjunction negation Property constraints universality existence cardinality Properties of properties transitivity symmetry 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 Language Comparison DTD XSD RDF S Bounded lists X is known to have exactly 5 children Cardinality constraints Kleene operators X X X X Class expressions unionOf complementOf X Data types Enumerations DAML OIL X X X X X Equivalence properties classes instances X Formal semantics model theoretic axiomatic X Inheritance X X Inference transitivity inverse X Qualified contraints all children are of type person X Reification Cornell CS 502 X 20020307 X 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 Cornell CS 502 20020307 But modeling the way things are is not always enough ABC Modeling how things or their descriptions change Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 queryability 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 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 Cornell CS 502 20020307 Intellectual Property Notion of ability to copy is the determining factor Promote abstraction to work and actuality to manifestation and item Cornell CS 502 20020307