OpenHPI 4.2 - Ontologies in Computer Science

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OpenHPI 4.2 - Ontologies in Computer Science

  1. 1. Semantic Web TechnologiesLecture 4: Knowledge Representations I 02: Ontologies in Computer Science Dr. Harald Sack Hasso Plattner Institute for IT Systems Engineering University of Potsdam Spring 2013 This file is licensed under the Creative Commons Attribution-NonCommercial 3.0 (CC BY-NC 3.0)
  2. 2. 2 Lecture 4: Knowledge Representations I Open HPI - Course: Semantic Web Technologies Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  3. 3. 163 02 Ontologies in Computer ScienceOpen HPI - Course: SemanticHarald Sack, Hasso-Plattner-Institut, Universität Potsdam Semantic Web Technologies , Dr. Web Technologies - Lecture 4: Knowledge Representations I
  4. 4. The Concept of Ontology in Computer Science164 "An ontology is an explicit, formal specification of a shared conceptualization. The term is borrowed from philosophy, where an Ontology is a systematic account of Existence. For AI systems, what ‘exists’ is that which can be represented.“ Thomas R. Gruber: A Translation Approach to Portable Ontology tomgruber.org Specifications.Knowledge Acquisition, 5(2):199-220, 1993. conceptualization: abstract model (domain, identified relevant concepts, relations) explicit: meaning of all concepts must be defined formal: machine understandable shared: consensus about ontology Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  5. 5. Conceptualization165 apply shared concept Concept symbolizes refers to Symbol Object stands for „Jaguar“ Ogden, Richards: The Meaning of Meaning: A Study of the Influence of Language upon Thought and of the Science of Symbolism (1923) Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  6. 6. 166 ep res ent ould we r How sh es? O nto logi Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  7. 7. Ontologies - Components and Models167 • Classes, Relations and Instances • Classes represent concepts • Classes are described via attributes • Attributes are name value pairs „The address contains the name, title, Address and place of residence of the person • given name <string > addressed“ • family name <strin g> • street <string> Informal Description • ZIP code <int> • city <string> •… Semi informal Description Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  8. 8. Ontologies - Components and Models168 • Classes are related to other classes has an Person Address is subclass of is subclass of Formal Definition: Sets m1,…mn Professor Student Relation R ⊆ m1 x … x mn gives visits Lecture Course is subclass of • Relations are special attributes, whose values are objects of (other) classes Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  9. 9. Ontologies - Components and Models169 • For Relations and Attributes Constraints (Rules) can be defined that determine allowed values is subclass of Woman has Person Address ≠ is subclass of 1:n Man is subclass of is subclass of 1:1 Professor Student Woman ⋂ Man = ∅ Constraint Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  10. 10. Ontologies - Components and Models1610 • Classes, relations, and constraints can be put together to form statements / assertions • Special Case: formal Axioms Example: • „it is not possible to lecture two courses at the same time“ • Axioms describe knowledge that can‘t be expressed simply with the help of other existing components. Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  11. 11. Ontologies - Components and Models1611 • Instances describe individuals of an ontology Course is subclass of Seminar Seminar Linked Data is a Application Engineering takes place at is located at Thursday A-2.1 11.00 pm Individuals (instances) are the basic components of an ontology. The individuals in an ontology may include concrete objects such as people, animals, tables, automobiles, molecules, and planets, as well as abstract individuals such as numbers and words. Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
  12. 12. 1612 03 How do I define a formal model of an ontology?Open HPI - Course: SemanticHarald Sack, Hasso-Plattner-Institut, Universität Potsdam Semantic Web Technologies , Dr. Web Technologies - Lecture 4: Knowledge Representations I

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