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Ontologies

Ontologies. Lecture Notes Prepared by Jagdish S. Gangolly Interdisciplinary Ph.D Program in Information Science State University of New York at Albany. Ontology.

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Ontologies

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  1. Ontologies Lecture Notes Prepared by Jagdish S. Gangolly Interdisciplinary Ph.D Program in Information Science State University of New York at Albany Inf 722 Information Organisation (Fall 2007) (Gangolly)

  2. Ontology • “…ontology is a data model that represents a set of concepts within a domain and the relationships between those concepts. It is used to reason about the objects within that domain.” -- Wikipedia Inf 722 Information Organisation (Fall 2007) (Gangolly)

  3. Ontology • Representation of shared conceptualisations • Representation of knowledge regarding a domain, or a part of the world Inf 722 Information Organisation (Fall 2007) (Gangolly)

  4. Ontology • Quine’s ontological commitment: “To be is to be the value of a variable” • Ontological reduction: The most economical ontology for a purpose Inf 722 Information Organisation (Fall 2007) (Gangolly)

  5. Ontology • Criteria of identity: “No entity without identity” • “On the Ontological Remarks on the Propositional Calculus”, “A Logical Approach to the Ontological Problem”, and “On What There Is” Quine Inf 722 Information Organisation (Fall 2007) (Gangolly)

  6. Ontology • “We may be said to countenance such and such an entity if and only if we regard the range of our variables as including such an entity. To be is to be a value of a variable” Quine Inf 722 Information Organisation (Fall 2007) (Gangolly)

  7. Ontology • “What entities there are, from the point of view of a given language, depends on what opositions are accessible to variables in that language…. There is one important sense, however, in which the ontological question transcends linguistic convention: How economical an ontology can we achieve and still have a language adequate to all purposes of science? In this form the question of ontological presuppositions of science survives.” Quine Inf 722 Information Organisation (Fall 2007) (Gangolly)

  8. Ontology Development 101 • The remaining slides are based on the above article available at:http://protege.stanford.edu/publications/ontology_development/ontology101-noy-mcguinness.html Inf 722 Information Organisation (Fall 2007) (Gangolly)

  9. Why Ontology • To share common understanding of the structure of information among people or software agents • To enable reuse of domain knowledge • To make domain assumptions explicit • To separate domain knowledge from the operational knowledge • To analyze domain knowledge Inf 722 Information Organisation (Fall 2007) (Gangolly)

  10. Ontology • Knowledge Representation • Semantic networks (directed graphs with concepts as nodes and relationships as arrows) • Frames (A frame is a collection of attributes or slots and associated values that describe some real world entity) Inf 722 Information Organisation (Fall 2007) (Gangolly)

  11. Ontology • Predicate/Propositional Logic • Work on ontologies grew out of research on building a logical basis for semantic networks and Frames. Such basis needed to be decidable Inf 722 Information Organisation (Fall 2007) (Gangolly)

  12. Ontology • Bell Labs prototype CLASSIC was the first attempt at such work. • A fragment of first order logic, called Descriptive Logics, is such a basis Inf 722 Information Organisation (Fall 2007) (Gangolly)

  13. Ontology • Light-weight ontologies can be developed using the methods of Thesauri and also Object-Oriented systems design such as, for example, UML (Unified Modeling Language) Inf 722 Information Organisation (Fall 2007) (Gangolly)

  14. Ontology • Ontology Development • Domain of discourse • Concepts or Classes • Slots or Roles or Properties • Slot/Role restrictions • Instances Inf 722 Information Organisation (Fall 2007) (Gangolly)

  15. Ontology • There is no one correct way to model a domain • Ontology development is necessarily an iterative process. • Concepts in the ontology should be close to objects (physical or logical) and relationships in your domain of interest. These are most likely to be nouns (objects) or verbs (relationships) in sentences that describe your domain. Inf 722 Information Organisation (Fall 2007) (Gangolly)

  16. Ontology Development Steps • Step 1. Determine the domain and scope of the ontology • Step 2. Consider reusing existing ontologies • Step 3. Enumerate important terms in the ontology • Step 4. Define the classes and the class hierarchy • Step 5. Define the properties of classes—slots • Step 6. Define the facets of the slots • Step 7. Create instances Inf 722 Information Organisation (Fall 2007) (Gangolly)

  17. Step 1. Domain and scope of the ontology • What is the domain that the ontology will cover? • For what we are going to use the ontology? • For what types of questions the information in the ontology should provide answers? • Who will use and maintain the ontology? Inf 722 Information Organisation (Fall 2007) (Gangolly)

  18. Step 1. Domain and scope of the ontology • Make a list of questions that the knowledge base should answer. • Evaluation: Does the ontology answer all those questions? Inf 722 Information Organisation (Fall 2007) (Gangolly)

  19. Step 2. Consider reusing existing ontologies • Ultimately, your ontology will need to interface with existing ontologies. So, a good idea to reuse them Inf 722 Information Organisation (Fall 2007) (Gangolly)

  20. Step 2. Consider reusing existing ontologies • Some Sources • Ontolingua ontology library (http://www.ksl.stanford.edu/software/ontolingua/) • DAML ontology library (http://www.daml.org/ontologies/) • publicly available commercial ontologies (e.g., UNSPSC (www.unspsc.org), RosettaNet (www.rosettanet.org), DMOZ (www.dmoz.org) Inf 722 Information Organisation (Fall 2007) (Gangolly)

  21. Step 3. Enumerate important terms in the ontology • Use methods we have discussed in the class Inf 722 Information Organisation (Fall 2007) (Gangolly)

  22. Step 4. Define the classes and the class hierarchy • Top-down • Bottom-up • A Combination Inf 722 Information Organisation (Fall 2007) (Gangolly)

  23. Step 5. Define the properties of classes—slots • “intrinsic” properties such as the flavor of a wine • “extrinsic” properties such as a wine’s name, and area it comes from • parts, if the object is structured; these can be both physical and abstract “parts” (e.g., the courses of a meal) • relationships to other individuals; these are the relationships between individual members of the class and other items (e.g., the maker of a wine, representing a relationship between a wine and a winery, and the grape the wine is made from.) Inf 722 Information Organisation (Fall 2007) (Gangolly)

  24. Step 6. Define the facets of the slots • Slot cardinality -- Slot cardinality defines how many values a slot can have • Slot-value type -- A value-type facet describes what types of values can fill in the slot Inf 722 Information Organisation (Fall 2007) (Gangolly)

  25. Step 6. Define the facets of the slots • Domain and range of a slot • Allowed classes for slots of type Instance (Range) • The classes to which a slot is attached or a classes which property a slot describes (Domain) Inf 722 Information Organisation (Fall 2007) (Gangolly)

  26. Step 7. Create instances • Choosing a class • Creating an individual instance of that class • Filling in the slot values Inf 722 Information Organisation (Fall 2007) (Gangolly)

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