CS690L - Lecture 3 1 CS690L Semantic Web and Knowledge Discovery: Concept, Technologies, Tool Yugi Lee STB #555 (816) This presentation was designed based on Richard Fikes’s tutorial on Ontologies and Semantic Web.

2 CS690L - Lecture 3 Semantic Web Language XML Language for describing the structure of document content e.g., declare data to be a retail price, a sales tax, a book title,... Uniform method for describing and exchanging data using HTTP Provides a “syntactic schema” From Semistructured Data... Language R. Goldman Proceedings of... Databases Location of what? Philadelphia Pennsylvania June 1999 When in June?

3 CS690L - Lecture 3 Semantic Web Language XML Is Not Enough –Ontologies enable independently developed programs to exchange data: XML provides “syntactic schema” –Ontologies specify intended meaning in a computer interpretable form: XML provides no means of specifying intended meaning of tags “XML is like HTML, where you make up your own tags.” “But in XML, you can’t say what your tags mean.”

4 CS690L - Lecture 3 W3C Semantic Web Activity Semantic Web Activity ( –“Established to serve a leadership role, in both the design of enabling specifications and the open, collaborative development of technologies that support the automation, integration and reuse of data across various applications.” –Successor to the W3C Metadata Activity RDF Core Working Group ( –Responsible for the Resource Description Framework (RDF) Web Ontology Working Group ( –Charter: Build upon the RDF Core work a language for defining structured web based ontologies which will provide richer integration and interoperability of data among descriptive communities –Developing Ontology Web Language (OWL): Based on DAML+OIL, developed in DARPA’s Agent Markup Language program

5 CS690L - Lecture 3 Resource Description Framework (RDF) A simple representation language for describing Web resources All sentences are triples of the form “(Property Subject Object)” –Property is a binary relation –Subject is a URI reference –Object is either a URI reference or a literal E.g., (creatorOf “Ora Lassila”) XML external syntax, Model theoretic semantics Includes a resource “Class” and properties “type”, “subclassOf”, etc. –Supports classes of resources and literals: (type Elephant Clyde) –Supports subclass hierarchies: (subclassOf Elephant Mammal) Like a primitive frame representation language

6 CS690L - Lecture 3 RDF Ontology Classes –Resource –Property –Literal –Statement –Container Bag Seq Alt Properties –type –subject –predicate –object

7 CS690L - Lecture 3 RDF Schema  Properties  subClassOf  subPropertyOf  seeAlso  isDefinedBy  comment  label  range  domain  member An ontology added to RDF  Classes  Class  ContainerMembershipProperty Resource ClassProperty ContainerMembershipPro perty Literal ContainerStatement Ba g Se q Alt

8 CS690L - Lecture 3 RDF-S Class and Property Definitions registeredTo Christine is a passenger vehicle. Is Christine a motor vehicle? Yes. Christine is registered to Arnie. What is Arnie? A person.

9 CS690L - Lecture 3 Comments on RDF and RDF-S Severely lacking in expressive power –Domain and range constraints rather than Value-Type E.g., can’t define class of people all of whose children are male –No cardinality constraints Particularly important for “exactly 1” and “at most 1” –No decompositions Particularly important for “disjoint” and “exhaustive” –No axioms –No negation (!) Not useful for checking consistency E.g., can’t prove an object is not an instance of a class Basically a typing system

10 CS690L - Lecture 3 The DAML Program DAML: DARPA Agent Markup Language Defense Advanced Research Agency (DARPA) program –Program Managers: James Hendler, Murray Burke –Begin in August 2000 Goal: achieve semantic interoperability between Web pages, databases, programs, and sensors Integration contractor and 16 technology development teams –MIT (Tim Berners-Lee, Ben Grosof) –Stanford (Gio Weiderhold, Richard Fikes, Deborah McGuinness) –UMBC (Tim Finin) –U West Florida (Pay Hayes) –Yale (Drew McDermott) …  Cycorp (Doug Lenat)  Nokia (Ora Lassila)  Teknowledge (Bob Balzer)  Web site:

11 CS690L - Lecture 3 DAML+OIL A representation language for user-defined ontologies –An ontology added to RDF and RDF-Schema –Specification document: Expressive power analogous to: –Description logics (e.g., CLASSIC) –Monotonic frame languages (e.g., OKBC knowledge model) Designed in collaboration with the European Community Designers of the Ontology Inference Layer (OIL) Basis for OWL, the candidate W3C standard

12 CS690L - Lecture 3 DAML+OIL Classes Thing Restriction List Ontology AbstractProperty TransitiveProperty DatatypeProperty UniqueProperty UnambiguousProperty Nothing

13 CS690L - Lecture 3 DAML+OIL Properties Equivalence equivalentTo, sameClassAs, samePropertyAs Lists first, rest, item Properties inverseOf Ontologies versionInfo, imports Classes disjointWith Defining Non-primitive classes unionOf, disjointUnionOf, intersectionOf, complementOf, oneOf Restrictions onProperty, toClass, hasValue, hasClass, hasClassQ minCardinality, maxCardinality, cardinality minCardinalityQ, maxCardinalityQ, cardinalityQ

14 CS690L - Lecture 3 Property Restrictions on Classes Person is a subclass of objects whose parents are persons. Person is a subclass of resources that have one father. 1 All objects all of whose parents are persons All objects that have exactly 1 father Person

15 CS690L - Lecture 3 Comments on DAML+OIL and OWL Expressive power of a description logic –Representation language for both classes and instances Additional expressive power needed (at least FOL) –No rationale for excluding any axiom from an ontology that is – Not a tautology Satisfied by the intended interpretation of the ontology –Example of need for additional expressive power “The magnitude of a physical quantity in a given unit of measure” (=> (AND (Quantity-Magnitude ?q ?u ?m) (Quantity-Dimension ?q ?d)) (AND (type Physical-Quantity ?q) (type Unit-Of-Measure ?u) (type Magnitude ?m) (Unit-Dimension ?u ?d))) May be too difficult for the Web community to understand –Acceptance will be depend on user-friendly tools Ok to support development of Semantic Web technology