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What is an Ontology?

What is an Ontology?. No exact definition A tool to help organize knowledge Or a way to convey a theory on how to represent a class of things Examples of definitions. Webster’s Dictionary. Webster’s Third New International Dictionary defines Ontology:

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What is an Ontology?

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  1. What is an Ontology? • No exact definition • A tool to help organize knowledge • Or a way to convey a theory on how to represent a class of things • Examples of definitions

  2. Webster’s Dictionary • Webster’s Third New International Dictionary defines Ontology: • A science or study of being specifically, a branch of metaphysics relating to the nature and relations of being. • A theory concerning the kinds of entities and specifically the kinds of abstract entities that are to be admitted to a language system.

  3. Philosophy • Dates back to 5th Century B.C. when Empedocles (490—c. 430 BCE) (http://en.wikipedia.org/wiki/Empedocles ) divided the world into four elements – earth, fire, water and air. • Aristotle’s (384—322 BCE) classification • Defined by philosophers as the nature of being “or” existence. • Branch of metaphysics • Entity categories and relationships • Often confused with the word epistemology, which is about knowledge and knowing

  4. Thomas Gruber • “An ontology is a specification of a conceptualization” • The conceptualization is an abstract and simplified view of the world you want to represent, which is specified in a format based on the relationships between them. • Examples: hierarchy, cluster, relational diagram

  5. The Role of Ontology • Basic Role: To provide a language which allows a group of people to share information reliably in a chosen area of work • OWL FAQ W3C http://www.w3.org/2003/08/owlfaq …[ontology] has become identified with computers as a machine readable vocabulary that is specified with enough precision to allow differing terms to be precisely related

  6. The Role of Ontology • Some areas of application • Indexing • Knowledge Sharing & Reuse • Artificial Intelligence (AI) • Enterprise Modeling • Software Design • Molecular Biology • eCommerce • Semantic Web….

  7. More on the Role of Ontology • Share common understanding of the structure of information among people and software agents • Enable reuse of domain knowledge • Make assumptions more explicit • Analyze domain knowledge

  8. Structure of Ontology • Most ontologies are structured as taxonomies or hierarchies • Basic ontology has two classes of elements: the entities and the relationships between them • Organized according to axioms or rules that control how the world will be defined.

  9. Important Facts • What exists is only what is represented in the ontology • Most ontologies focus on a specific area to conceptualize (e.g. subject thesauri) • Must be updated to keep up with dynamic world • No set discipline or methodology!

  10. SHOE Ontology project – • Possible to build an ontology for anything • Simple HTML Ontology Extensions (SHOE) Project (http://www.cs.umd.edu/projects/plus/SHOE/) • Ontology to organize the Web

  11. Ontologies from SHOE Beer Ontology http://www.cs.umd.edu/projects/plus/SHOE/onts/index.html#beer • Use existing ontologies for base definitions, i.e. organizations, liquid, event • Assume inheritance • Document Ontology http://www.cs.umd.edu/projects/plus/SHOE/onts/docmnt1.0.html

  12. Additional Ontologies • WordNet http://www.cogsci.princeton.edu/~wn/ • Sharable Ontology Library http://www-ksl-svc.stanford.edu:5915/ • UMDL Ontology Concept Descriptions http://www-personal.umich.edu/~peterw/Ontology/ontology.html

  13. Ontology continuum Classical view of ontology/language <___|____|_______|______I______I______I__> Simple thesauri/ deeper taxonomies low level full/intricate Key word CV thesauri onotologies ontologies Lists (WordNet)(OWL) Formal Ontologies

  14. Another ontology continuum (D.L. McGuinness, 2003)

  15. Basic steps for constructing an Ontology • Determine the scope and establish boundaries • W,w, w, w… (who what where when…?) • Implementation environment • Check for existing ontologies – borrow or build • Determine • categories, top nodes, • specific instances bottom up, or • combination approach

  16. Basic steps for constructing an Ontology • Identify vocabulary [concept] sources • Determine relationships, organic • (can have more than 1 type relationship) • Build… and grow • Link to other ontologies • Test the effectiveness

  17. Ontologies and logic First Order Predicate Logic • Inferences Man is mortal Aristotle is a man ___________________ .̇. Aristotle is mortal

  18. Another FOPL example (First Order Predicate Logic) Ndenotes unread e-mail Nappears by message yin inboxx ___________________ .̇. Message yis………. (an unread e-mail)

  19. Multiple inheritance (p. 13 of ontology 101) • A class can be a subclass of several classes • Suppose you want a class Dessert wine • Port is both a Red wine and a Dessert wine • Port, therefore, has to be defined as having two superclasses: Red wine and Dessert Wine Red wine Dessert wine Port

  20. Multiple inheritance (p. 13 of ontology 101) • .̇. All instances of the Port class are instances of both Red wine and Dessert Wine • Port will inherit its slots and their facets from both parents • Value of sweet, from sugar slot from the “Dessert wine class” • Value of for color of “red” from “Tannin level slot” for “Red wine class”

  21. Unified Medical Language System (UMLS) http://umlsks.nlm.nih.gov/kss/servlet/Turbine/template/admin,user,KSS_login.vm

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