1 semantic web & ontology reyhan aydoğan 20/02/2007
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Semantic Web & Ontology
Reyhan Aydoğan20/02/2007
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Semantic Web Information on the Web
Both human and machine understandable Deal with
Presentation of information Meaning of content and structure
Example Applications [1] Task-Centered Knowledge Support through
Semantic Markup Semantic Gadget in a museum Advance Search Engines
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Example 1 [2]
Search the web for performing particular task The system understands the task of users and
gives better service in order to achieve the goal.
E.g. when the user search the car keyword, if the system can understand the user’s task is to repair the car, it can perform search in accordance with the task instead of a general search.
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Example 1: Two dimensions
Anticipatability: measures the how easy or difficult to anticipate the question US History “Who was the 19th U.S. present” Easy “Is Pat Hayes related to Rutherford Hayes” Difficult
Frequency of occurrence: Who the current U.S. president is, is more frequent
than who the 19th U.S. president is. By limiting the domain, we can better
anticipate the kinds of tasks people working on.
Support in the frequently asked and moderately anticipatable questions.
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Example2 [3]
Apply Semantic Web onto Ubiquitous Computing Semantic gadget in a museum Guide and recommend in accordance
with environmental conditions with using semantics
If the temperature is too warm and we do not like to carry our coat, the gadget may suggest leaving it in the car
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Ontology “Specification of concepts and their
meanings” Shared and common understanding
of knowledge concerning domain of interests
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Gruber Ontology Definition
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Describing Semantics [4]
Individual
PropertyClass
Wine
ChateauMorgonBordeaux
hasColor
is an instance of
has value for
restrict
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Class Construct
The ontological class concept Related to Object class in OOP
Class Represents a group of individuals
with similar property Eg. Food, Wine, Person,
Restaurant
Class
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Property Construct Property construct associates
Attribute/ value pairs with instances Binary association relating an instance
to another instance or a simple data value
E.g. price, size, name, color Similar to accessor method in OOP
But, a property can be associated with multiple unrelated classes rather than a single class
Property
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Individuals Individuals represent
Class object instances in the domain Similar to objects in OOP
But individuals are only information representations and not have associated functionality
E.g. Mark, MyPieSlice, KnightRestaurant “It is difficult to differentiate between
individuals and classes” [4]
Individual
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Meanings
<Sentence><Subject>
Wine</Subject><Verb>
is made from</Verb><Object>
Grape </Object>
</Sentence>
DocumentOntology
Natural Language
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Ontology Main elements of an ontology:
Concepts Relationships
Hierarchical Logical
Properties Instances (individuals)
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Semantic Relationships [4]
Synonymy Relation (Equivalence) Two names for the same meaning Eg. “Restaurant and “Eating
Establisment” [class-class] “Cost” and “price” [property-property] “John Smith” and
“Restaurant123Owner”[individual-individual]
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Semantic Relationships cont.
Antonymy Relation Identifies opposite concepts Disjointness: An item cannot be an
instance of both of the disjoint items E.g. “Regular Priced Menu Item” and
“Sale Priced Menu Item”
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Semantic Relationships cont.
Hyponymy Relation (is-a relationship) Specialization or generalization Taxonomical hierarchies
Dessert
Pie Cake
Specialization
Generalization
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Semantic Relationships cont.
Meronymy/Holonymy Relation Part-of relation Defines composition or part-of
relationsSpaghetti and Meatballs Dish
Spaghetti Meatballs
Holonymy Meronymy
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RDF (Resource Description Framework)
Simple language Captures statements
Triples of <subject, predicate, object> E.g. <Eric Miller, hasTitle, Dr. >
Express the content itself Resources uniquely identified to
prevent confusion
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Example= Resources (URI)
=Literals
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Xml-based syntax
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Example <?xml version="1.0"?><RDF> <Description about="http://www.w3schools.com/RDF"> <author>Jan Egil Refsnes</author><homepage>http://www.w3schools.com</homepage></Description> </RDF> Subject: "http://www.w3schools.com/RDF"> Predicate : author Object: Jan Egil Refsnes
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Attributes
The <rdf:Description> element contains the description of the resource identified by the rdf:about attribute.
<rdf:ID> is for identification of resource where <rdf:about> is for referring a resource.
Rdf:type specifies the type of subject
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RDF Schema Language for describing RDF vocabulary Extension of RDF RDF talks about the object where RDF
Schema defines classes for objects Be able to represent a hierarchy of
classes “subClassOf” property
Use some constraints on properties Domain and range
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Example <?xml version="1.0"?><rdf:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntaxns#" xmlns:rdfs=http://www.w3.org/2000/01/rdf-schema#xml:base= "http://www.animals.fake/animals#"><rdf:Description rdf:ID="animal"><rdf:type
rdf:resource="http://www.w3.org/2000/01/rdfschema#Class"/>
</rdf:Description><rdf:Description rdf:ID="horse"> <rdf:type
rdf:resource="http://www.w3.org/2000/01/rdfschema#Class"/>
<rdfs:subClassOf rdf:resource="#animal"/> </rdf:Description></rdf:RDF>
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SubClassOF
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RDF Schema Example
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Discussion from 494 course slide [Pinar Yolum] JAVA: Class book has an attribute author of typeperson RDF: There is an author property between a bookand a person JAVA: If you are talking about a newspaper, youneed to define a new author attribute (Local scope) RDF: Define an author property once. (Globalscope) JAVA: You can’t talk about an author attributewithout a class RDF: You can if you don’t specify a domain
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Discussion from 494 course slide [Pinar Yolum] JAVA:
– Class sportsarcticle has an attribute author of type male– Class newsarticle has an attribute author of type female
RDF: Cannot match different domains with ranges JAVA is prescriptive
- Won’t allow a male as the author of a news article RDF is descriptive; usage is application-dependent
– Enforce constraints (like JAVA)– If the author of a news article is not known infer female– Accept the existence of a news article without an author– Accept a news article with an editor attribute instead
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OWL
Web Ontology Language Two types of property
Data property: string, int and so on Object property has characteristics:
Symmetric Transitive Functional inverseOf Inverse functional
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Symmetric Property P(x,y) iff P(y,x)
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Transitive Property P(x,y) and P(y,z) implies P(x, z)
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Functional Property P(x,y) and P(x,z) implies y = z
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InverseOf P1(x,y) iff P2(y,x)
<owl:ObjectProperty rdf:ID="hasMaker"><rdf:type
rdf:resource="&owl;FunctionalProperty" /></owl:ObjectProperty> <owl:ObjectProperty
rdf:ID="producesWine"> <owl:inverseOf rdf:resource="#hasMaker" />
</owl:ObjectProperty>
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Property Constraints
allValuesFrom, someValuesFrom <owl:onProperty rdf:resource="#hasMaker" />
<owl:allValuesFrom rdf:resource="#Winery" />
cardinality <owl:onProperty rdf:resource="#hasVintageYear"/>
<owl:cardinality rdf:datatype="&xsd;nonNegativeInteger">1
</owl:cardinality>
hasValue <owl:onProperty rdf:resource="#hasSugar" />
<owl:hasValue rdf:resource="#Dry" />
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Others Disjoint
Equivalence <owl:Class rdf:ID="TexasThings"> <owl:equivalentClass> <owl:Restriction> <owl:onProperty rdf:resource="#locatedIn" />
<owl:someValuesFrom rdf:resource="#TexasRegion" /> </owl:Restriction>
</owl:equivalentClass> </owl:Class>
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SPARQL: Query Language
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Conclusion
Ontology Tool Protégé
Ontology API KAON2 & JENA
Query Language: SPARQL
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References [1] Fensel, D., J. Hendler, H. Lieberman and W. Wahlster,
Spinning the Semantic Web, MIT Press, Cambridge, 2003. [2] Jasper, R. and M. Uschold, “Enabling Task-Centered
Knowledge Support though Semantic Markup”, In Spinning the Semantic Web, pp. 223-251, MIT Press, Cambridge,2003.
[3] Lassila, O. and M. Adler, “Ubiquitous Computing Meets the Semantic Web”, In Spinning the Semantic Web, pp. 363-376, MIT Press, Cambridge, 2003.
[4] Lee, W. L. , OWL: Representing Informaton Using the Web Ontology Language, Trafford Publishing, 2005.
[5] Munindar P. Singh and Michael N. Huhns, Service-Oriented Computing: Semantics, Processes, Agents, Wiley, 2004
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References For examples:
http://www.w3schools.com/ [5] Service-Oriented Computing: Semantics, Processes,
Agents
Discussion http://www.cmpe.boun.edu.tr/courses
/cmpe494/fall2005/slides/soc-slides-rdf.pdf
OWL http://www.w3.org/TR/owl-guide/