tutorial 1-ontologies

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]


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


A. C. LiangFAO, UN

27 April 2004

Where does it come from?

ontology n.

1692; lat. phil. onto- “being” + -logia “study of”


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).


A. C. LiangFAO, UN

27 April 2004


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?



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.


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


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


A. C. LiangFAO, UN

27 April 2004





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


A. C. LiangFAO, UN

27 April 2004





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


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


A. C. LiangFAO, UN

27 April 2004





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?


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


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


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


A. C. LiangFAO, UN

27 April 2004

Develop an ontology

• Map relations between upper and lower-level ontological items.


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


A. C. LiangFAO, UN

27 April 2004

Develop an ontology

• Choose an appropriate ontology language.– RDF– RDFS– OWL


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.


A. C. LiangFAO, UN

27 April 2004





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


A. C. LiangFAO, UN

27 April 2004


• 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


A. C. LiangFAO, UN

27 April 2004


• 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>


A. C. LiangFAO, UN

27 April 2004


• No systematic semantics, esp. in terms of hierarchy


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


A. C. LiangFAO, UN

27 April 2004


• Inferencing is possibleAssertions:

{ Dolly } instanceOf { BlueSheep }

{ BlueSheep } hasMother { BlueSheep }

{ Dolly } hasMother { Kristine }

Inference:– { Kristine } instanceOf { BlueSheep }


A. C. LiangFAO, UN

27 April 2004


• But still not expressive enough– No domain/range constraint at the local

level– No cardinality constraints– No transitive, symmetrical, inverse

properties


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,


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.


A. C. LiangFAO, UN

27 April 2004


• 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.


A. C. LiangFAO, UN

27 April 2004


• 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


A. C. LiangFAO, UN

27 April 2004

• Questions?

• References:– www.w3.org– Ontology resources

Thank you for coming.

tutorial 1-ontologies

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