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5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Tutorial 1:Ontologies
Fifth AOS Workshop
27 April 2004
Friendship HotelBeijing CHINA
Anita Liang (梁华英 ) [email protected]
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology, anyway?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology, anyway?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Where does it come from?
ontology n.
1692; lat. phil. onto- “being” + -logia “study of”
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Where does it come from?• Philosophy
– The study of what is, what has to be true for something to exist, the kinds of things that can exist
• AI and computer science– Co-opted the term. Something exists if it
can be represented, described, defined (in a formal, hence, machine-interpretable way).
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
A Definition
“a specification of a conceptualization…a description (like a formal specification of a program) of the concepts and relations that can exist for an agent or a community of agents.”
-T.R. Gruber. 1993. A translation approach to portable
ontologies. Knowledge acquisition, 5(2):199-220.
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
A Definition • Informal
– Terms • from a specific domain• uniquely defined, usually via natural language definitions
– May contain additional semantics in the form of informal relations
– machine-processing is difficult– Examples
• Controlled vocabulary• Glossary• Thesaurus
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
A Definition• Formal
– Domain-specific vocabulary– Well-defined semantic structure
• Classes/concepts/types– E.g., a class { Publication } represents all publications– E.g., a class { Publication } can have subclasses { Newspaper },
{ Journal }• Instances/individuals/objects
– E.g., the newspaper Le Monde is an instance of the class { Newspaper } • Properties/roles/slots
– Data» E.g., the class { Publication } and its subclasses { Newspaper },
{ Journal } have a data property { numberOfPages }– Object
» E.g., the class { Publication } and its subclasses { Newspaper }, { Journal } have an object property { publishes }
– Is machine-processable
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology, anyway?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Why develop ontologies?• To share knowledge
– E.g., using an ontology for integrating terminologies• To reuse domain knowledge
– E.g., geography ontology– E.g., AOS
• To make domain assumptions explicit– Facilitate knowledge management
• E.g., { BSE } –causedBy-> { Prion } ????– Enable new users to learn about the domain
• E.g., food safety ontology
• To distinguish domain knowledge from operational knowledge– e.g., biblio metadata
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology, anyway?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
What they are good for
• Informal– Controlled vocabulary
• Beginnings of interoperability
– Upper-level structures for extending further• E.g., AGRIS/CARIS categorization
– Browsing support• E.g., IRS information search
– Search• Limited query expansion
– disambiguation• E.g., vessels
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
What they are good for• Formal
– Search• Concept-based query
– User uses own words, language
• Related terms
• Intelligent query expansion: “fishing vessels in China” expands to “fishing vessels in Asia”
– Consistency checking• Restrictions on properties can allow checking of validity of
values
– Interoperability support• Terms defined in expressive ontos allow for mapping precisely
how one term relates to another
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology, anyway?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Research– What is the domain?– What is the scope?– What will it be used for?– Who will be the users?
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Develop upper-ontology categories, e.g., concepts “process,” “state”– Use what is already available
• E.g., SUMO, Cyc, WordNet
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Develop a domain-specific lexicon– Reuse one or more pieces of already
existing resources• E.g., Agrovoc• Modify and extend
– Compile large domain-specific text corpus and use tools to help identify/extract domain-specific terms
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Define classes and properties– Classes should correspond closely to
nouns in the domain; properties correspond roughly to verbs.
• Define class hierarchy– Top-down analysis, bottom-up analysis– Combination
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Map relations between upper and lower-level ontological items.
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• WWW resources– www.taxonomywarehouse.com– www.dmoz.com– protégé.stanford.edu/ontologies/ontologies.html– directory.google.com/top/reference/
knowledge_management/knowledge_representation/ontologies
– www.nlm.nih.gov/research/umls– www.cyc.com– www.slais.ubc.ca/resources/indexing/
database1.htm#online
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Choose an appropriate ontology language.– RDF– RDFS– OWL
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Develop an ontology
• Develop evaluation method.– Test for consistency, completeness
through application development and debugging.
– Use subject matter experts to evaluate.
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
1. Where does the notion of ontology come from?
2. What exactly is an ontology, anyway?3. Why develop an ontology?4. What can an ontology be used for ?5. How can I develop one?6. Which language should I choose?
What this talk is about
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework
• RDF is– a formalism for representing metadata– a way to describe the semantics of
information
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework
• RDF data model– Resource
• The basic unit being described, includes any object such as website, document, picture, etc.
• Identified via URI– Property
• Characteristic of a resource• Also identified via URI
– Statement• Describes properties of resources • Triples: <Subject, Predicate, Object>
• URI– Uniform Resource Identifier– Used for uniquely identifying resources
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework
• Syntax– Based on xml– <Description> element describes a
resource– Attribute or nested element describes a
property<rdf:Property rdf:ID=“afflicts”></ rdf:Property >
<rdf:Description rdf:about=“http//:www.fao.org/aos/bse”>< afflicts resource=“http//:www.fao.org/aos/cow”>
</ afflicts>
</rdf:Description>
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework
• No systematic semantics, esp. in terms of hierarchy
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework Schema
• Allows for interpretation of resources• Some RDFS terms:
– Class• Defines categories into which resources can be
grouped
– subClassOf• Allows the creation of hierarchy of classes
– Domain, range• Constrains the classes that can be subject and
object of property, respectively
– subPropertyOf• Properties can be inherited
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework Schema
• Inferencing is possibleAssertions:
{ Dolly } instanceOf { BlueSheep }
{ BlueSheep } hasMother { BlueSheep }
{ Dolly } hasMother { Kristine }
Inference:– { Kristine } instanceOf { BlueSheep }
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Resource Description Framework Schema
• But still not expressive enough– No domain/range constraint at the local
level– No cardinality constraints– No transitive, symmetrical, inverse
properties
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Web Ontology Language (OWL)
• OWL consists of all elements and attributes provided by RDF and RDFS, but goes beyond, allows greater inferencing capabilities.– allows info to be gathered from distributed sources– instance document can be enhanced with an OWL
property to indicate that it’s the same as another instance. For example,
• Police report shows that Sam is suspected of being a drug king.
– Sam suspectedOf drug king • FBI file shows that Tony is a mafia boss
– Tony suspectedOf mafia• CIA has a file on Tony.
– Tony owl:sameIndividualAs Sam• Inference: the drug king is the same as the mafia boss,
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Web Ontology Language (OWL)• OWL consists of all elements and attributes provided by
RDF and RDFS, but goes beyond, allows greater inferencing capabilities.– provides capability of constructing taxonomies which can be
used to dynamically understand how an instance relate to other entities1. User: Is Virago a motorcycle?2. Web agent goes to websites: Send me your catalog.3. Catalog contains:
<custom rdf:ID=“Virago”><size>535 cc</size><cylinder>2</cylinder>
</custom> 4. Web agent consults ontology:
{ Sport } subClassOf { Motorcycle }{ Custom } subClassOf { Motorcycle } { Grand Tourism } subClassOf { Motorcycle }
5. Inference: The Virago is a custom motorcycle.
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Web Ontology Language (OWL)
• OWL consists of all elements and attributes provided by RDF and RDFS, but goes beyond, allows greater inferencing capabilities.– provides capability of specifying that a property can
relate a resource to a specific number of other resources; 1. User: What is Jill’s birthplace?2. { Person } –hasBirthplace-> 1 { Location }2. Three different documents found:
Document A: { Jill } hasBirthplace { Texas }Document B: { Jill } hasBirthplace { Lone Star State }Document C: { Jill } hasBirthplace { Middle of Nowhere }
3. Inference: Texas, Lone Star State, and Middle of Nowhere all refer to the same location.
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
Web Ontology Language (OWL)
• Owl Lite– Classification hierarchy, simple
constraints, e.g., cardinality is 1 or 0
• Owl DL– Maximum expressivity and also
computationally complete
• OWL Full– Maximum expressivity but no
computational guarantees
5th AOSWorkshopBeijing
A. C. LiangFAO, UN
27 April 2004
• Questions?
• References:– www.w3.org– Ontology resources
Thank you for coming.