The Semantic Web #8 - Ontology

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This is a lecture note #8 for my class of Graduate School of Yonsei University, Korea. It describes what ontology is and its representation scheme.

Transcript of The Semantic Web #8 - Ontology

  • 1. Linked Data &Semantic WebTechnology The Semantic Web Part 8. Ontology Dr. Myungjin Lee
  • 2. Ontology Origin of Ontology onto : "being; that which is logy - : "science, study, theory Ontology in Philosophy the philosophical study of the nature of being, becoming, existence, or reality, as well as the basic categories of being and their relations what entities exist or can be said to exist how such entities can be grouped, related within a hierarchy 2Linked Data & Semantic Web Technology
  • 3. Types of Ontology Upper ontology concepts supporting development of an ontology, meta-ontology Domain ontology concepts relevant to a particular topic or area of interest, for example, information technology or computer languages, or particular branches of science Interface ontology concepts relevant to the juncture of two disciplines Process ontology inputs, outputs, constraints, sequencing information, involved in business or engineering processes 3Linked Data & Semantic Web Technology
  • 4. Ontology in Information Science What is Ontology? to represent knowledge as a set of concepts within a domain, and the relationships between pairs of concepts "formal, explicit specification of a shared conceptualisation" by Thomas R. Gruber shared to represent consensual knowledge conceptualisation abstract model formal machine readable, processible, and understandable explicit fully and clearly expressed 4Linked Data & Semantic Web Technology
  • 5. Conceptualization What is Conceptualization? the process of development and clarification of concepts Object refer to stand for Concept symbolize Namdeamun Symbol 5Linked Data & Semantic Web Technology
  • 6. Component of Ontology Class concepts that are also called type, sort, category, and kind Vehicle, the class of all vehicles Property characteristics that objects (and classes) can have 6-speed transmission Relationship how objects are related to other objects Ford Explorer is defined as a successor of : Ford Bronco Restriction formally stated descriptions of what must be true in order for some assertion to be accepted as input door (with as minimum and maximum cardinality: 4) Axiom assertions in a logical form that together comprise the overall theory that the ontology describes in its domain of application Instance the basic, "ground level" components of an ontology Ford Explorer object 6Linked Data & Semantic Web Technology
  • 7. How to Represent Ontology Logic the study of modes of reasoning (which are valid, and which are fallacious) Topics in Logic Propositional Logic First Order Logic Description Logic 7Linked Data & Semantic Web Technology
  • 8. Propositional Logic a formal system in which formulas of a formal language may be interpreted as representing propositions How to model facts? Simple Assertions Modeling The moon is made of green cheese g It rains r The street is getting wet. n Simple Assertions Modeling if it rains, then the street will get wet. rn If it rains and the street does not get wet, (r n) g then the moon is made of green cheese. not powerful enough to represent all types of assertions 8Linked Data & Semantic Web Technology
  • 9. First Order (Predicate) Logic Predicate Logic logic using a verb phrase template that describes a property of objects, or a relationship among objects represented by the variables "x is blue" blue(x) the existential ("there exists") and universal ("for all") quantifiers "for every object x in the universe, x > 1" (x) x > 1 First Order Logic predicate logic that individuals can be quantified only FOL contains Objects : people, houses, numbers, theories, Ronald McDonald, Relations : red, round, bogus, prime, brother of, bigger than, inside, . Functions : father of, best friend, third inning of, one more than, end of 9Linked Data & Semantic Web Technology
  • 10. First Order Logic Syntax of FOL: Basic elements Constants KingJohn, 2, UCB, Predicates Brother, >, Functions Sqrt, LeftLegOf,.. Variables x, y, a, b, Connectives Equality = Quantifiers , How to model facts? the father of a person is a male parent. x y: isFather(x, y) (Male(x) isParent(x, y)) 10Linked Data & Semantic Web Technology
  • 11. First Order Logic FOL is perfectly suited for the description of ontologies, but FOL is high expressivity too bulky for modeling not appropriate to find consensus in modeling proof theoretically very complex (semi-decidable) 11Linked Data & Semantic Web Technology
  • 12. Description Logic What is Description Logic? fragment of FOL a family of formal knowledge representation languages for representing information about individuals, classes of individuals and their description more expressive than propositional logic but has more efficient decision problems than first-order predicate logic FOL DL class concept property or predicate role object individual 12Linked Data & Semantic Web Technology
  • 13. Concepts of Description Logic The core is a concept language use it for expressing factual assertions, intentional knowledge and queries Concepts denote entities, classes Student { x | STUDENT(x) } Roles denote properties, relations F