cs690l - lecture 3 1 cs690l semantic web and knowledge discovery: concept, technologies, tool yugi...
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CS690L - Lecture 31
CS690LSemantic Web and Knowledge Discovery: Concept, Technologies, Tool
Yugi LeeSTB #555(816) [email protected]/~leeyu
This presentation was designed based onRichard Fikes’s tutorial on Ontologies and Semantic Web.
2CS690L - 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”
<Publication URL = "ftp://db.stanford … xml.ps”> <Title> From Semistructured Data ... Language </Title> <Author> R. Goldman </Author> <Published> Proceedings of ... Databases </Published> <Location> Location of what?Location of what? <City> Philadelphia </City> <State> Pennsylvania </State> </Location> <Date> <Month> June </Month> <Year> 1999 </Year> </Date></Publication>
When in June?When in June?
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Semantic Web Language
XML Is Not Enough – Ontologies enable independently developed programs Ontologies enable independently developed programs
to exchange data: XML provides “syntactic schema”to exchange data: XML provides “syntactic schema”– Ontologies specify intended meaning in a computer Ontologies specify intended meaning in a computer
interpretable form: XML provides no means of interpretable form: XML provides no means of specifying intended meaning of tags 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.”
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W3C Semantic Web Activity
• Semantic Web Activity (http://www.w3.org/2001/sw/)– “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 (http://www.w3.org/2001/sw/RDFCore/)
– Responsible for the Resource Description Framework (RDF)
• Web Ontology Working Group (http://www.w3.org/2001/sw/WebOnt/)– 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
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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 literalE.g., (creatorOf http://www.w3.org/Lassila “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
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RDF Ontology
• Classes
– Resource
– Property
– Literal
– Statement
– Container
• Bag
• Seq
• Alt
• Properties– type
– subject
– predicate
– object
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RDF Schema
PropertiesProperties subClassOf
subPropertyOf
seeAlso
isDefinedBy
comment
label
range
domain
member
An ontology added to RDF ClassesClasses
Class
ContainerMembershipProperty
Resource
Class Property
ContainerMembershipProperty
Literal
Container Statement
Bag
Seq
Alt
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RDF-S Class and Property Definitions
<rdf:Class ID="MotorVehicle"> <rdfs:subClassOf rdf:resource="http.../PR-rdf-schema-19990303#Resource"/></rdf:Class>
<rdf:Class ID="PassengerVehicle"> <rdfs:subClassOf rdf:resource="#MotorVehicle"/></rdf:Class><rdf:Class ID="Van"> <rdfs:subClassOf rdf:resource="#MotorVehicle"/></rdf:Class><rdf:Class ID="MiniVan"> <rdfs:subClassOf rdf:resource="#Van"/> <rdfs:subClassOf rdf:resource="#PassengerVehicle"/> </rdf:Class><rdf:Property ID = "registeredToregisteredTo"> <rdfs:domain rdf:resource = “#MotorVehicle” />
<rdfs:range rdf:resource = “#Person” />
</rdf:Property>
Christine is a Christine is a passenger vehicle.passenger vehicle.
Is Christine a motor Is Christine a motor vehicle?vehicle?Yes.Yes.
Christine is registered Christine is registered to Arnie.to Arnie.
What is Arnie?What is Arnie?A person.A person.
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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
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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: http://www.daml.org/
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DAML+OIL
• A representation language for user-defined ontologies
– An ontology added to RDF and RDF-Schema
– Specification document:
http://www.daml.org/2000/12/daml+oil-index.html
• 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
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DAML+OIL Classes
Thing
Restriction
List
Ontology
AbstractProperty
TransitiveProperty
DatatypeProperty
UniqueProperty
UnambiguousProperty
Nothing
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DAML+OIL Properties
• EquivalenceequivalentTo, sameClassAs,
samePropertyAs
• Listsfirst, rest, item
• PropertiesinverseOf
• OntologiesversionInfo, imports
• ClassesdisjointWith
• Defining Non-primitive classesunionOf, disjointUnionOf, intersectionOf,
complementOf, oneOf
• RestrictionsonProperty, toClass, hasValue, hasClass, hasClassQ
minCardinality, maxCardinality, cardinality
minCardinalityQ, maxCardinalityQ, cardinalityQ
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Property Restrictions on Classes
<Class ID = "Person">
<comment> Person is a subclass of objects whose parents are persons. </comment>
<rdfs:subClassOf>
<daml:Restriction>
<daml:onProperty rdf:resource = “#hasParent” />
<daml:toClass rdf:resource = “#Person” />
</daml:Restriction>
</rdfs:subClassOf>
<comment > Person is a subclass of resources that have one father. </comment>
<rdfs:subClassOf>
<daml:Restriction>
<daml:onProperty rdf:resource = “#hasFather” />
<daml:cardinality> 1 </daml:cardinality>
</daml:Restriction>
</rdfs:subClassOf>
All objects all of whose
parents are persons
All objects that have exactly 1
father
Person
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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