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Semantic Web

Semantic Web. Quratulain Rajput Faculty of Computer Science, IBA Spring2013. Ontology. Ontology is the Greek word, philosophical study of the nature of being, existence, as well as basic categories of being and their relations.

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Semantic Web

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  1. Semantic Web Quratulain Rajput Faculty of Computer Science, IBA Spring2013

  2. Ontology • Ontology is the Greek word, philosophical study of the nature of being, existence, as well as basic categories of being and their relations. • ontology deals with questions concerning what entities exist or can be said to exist, and how such entities can be grouped, related within a hierarchy, and subdivided according to similarities and difference. [wikipedia] Quratulain Rajput

  3. Why Ontology • People cannot share knowledge, if they don’t understand the common language. • Thus, ontology provides common language to share knowledge. • The common language to share knowledge consist of : • Common symbol and concepts (Syntax) • Agreement about their meaning (Semantics) • Classification of concepts (hierarchy) • Associations and relations of concepts (Thesauri) • Rules and Knowledge about which relations are allowed and make sense(Ontologies) Quratulain Rajput

  4. What is knowledge? The philosopher Plato famously defined knowledge as: "justified true belief." However, no single agreed upon definition of knowledge exists, though there are numerous theories to explain it. Truths: Basic truth in the world, things that consider to be true. Belief: your beliefs, but not all belief are to be true. Knowledge: is a subset of all true beliefs. Truths Beliefs Knowledge Quratulain Rajput

  5. Ontologies • Ontologies are formal representation of knowledge. • In Greek Philosophical study: • Onto+logy= the study of the nature of being. What does exist and can be said to exist? • Define what is really true independent of our perception. • In philosophy Ontology is singular because it is a study while in Computer Science, it is for knowledge representations therefore more than one. Quratulain Rajput

  6. History of ontology • [400 BC] Greek philosopher Plato and Socrates posed the idea that: • Reality is completely different from what we perceived from our senses. • They say that the things we see in the real world (perception) are mutable/perishable. Time is important factor to show its mutability. • The individual perception are instances of ideas. Where ideas are immutable and only exist in our mind. • In computer science, ideas are class and object are instances of class. Thus, they laid the foundation of Object-Oriented Paradigm. perception idea Class/Model instance Quratulain Rajput

  7. History of ontology • [400 BC] Aristotle defines a system of general categories for classification of all things about which statement can be made of. • The porphyry presented the visualization of such classification to make it more understandable. • Structured explanation of the real world. Quratulain Rajput

  8. History • Aristotle also laid the foundation of formal logic (first-order-logic). Basics today’s logic. Premises All Arabs are Muslims All Muslims are Humans Conclusion: All Arabs are Humans Quratulain Rajput

  9. Islamic Logicians • Avicenna (IbnSina) (c. 980 - 1037) • [980-1037 AH ] IbnSīnāor by his Latinized name Avicenna, was a Persian. • More clearly distinguished between essence (Mahiat) and existence (Wujud) than Aristotle. • He reconcile rational philosophy with Islamic theology. His aim was to prove the existence of God and His creation of the world scientifically and through reason and logic. • Others are • Al Kindi (c. 801 - 873) • Al-Farabi (c. 872 - 950/951) • Averroes (IbnRushd) (1126 - 1198) [http://www.ontology.co/logic-medieval.htm] Quratulain Rajput

  10. History • Problem of Universals: • Do Universals ideas posses real existence (ontology). • For example there are some universal good or universal bad concept(heaven, evil). Does they really exist. • Two thoughts: • Realism: “Universals are real!“ • Nominalism: “Universals are nothing but words and symbols!“ Quratulain Rajput

  11. History • Logic and Grammar: according to Ramon Lull is “the art and the science to distinguish between truth or lie with the help of reason, to accept truth and to reject lie.“ Quratulain Rajput

  12. History • Inaccuracy in natural language. For example, used of same vocabulary with different meaning. • [1614-1672]John Wilkins, developed the idea of a universal philosophical Language with the goal to represent the entire knowledge of the universe. The idea was very challenging not carried out practically. • Gottfried Wilhelm Leibniz develops the idea of “characteristic numbers“ as a model rather than natural language. Quratulain Rajput

  13. Ontology in Computer Science An ontology is an explicit, formal specification of a sharedconceptualization. The term is borrowed from philosophy, where an ontology is a systematic account of Existence. For knowledge-based systems, what “exists” is exactly that which can be represented. • conceptualization: abstract model(domain, concepts, relations) • explicit: meaning of all concepts must be defined • formal: machine understandable • shared: consensus about ontology Tom Gruber http://tomgruber.org/writing/ontolingua-kaj-1993.pdf Quratulain Rajput

  14. Ontology in Computer Science • Ontology first used by Artificial intelligence researchers: • They create ontologies as computational models that enable certain kinds of automated reasoning. • In the 1980s, the AI community began to use the term ontology to refer to both a theory of a modeled world and a component of knowledge systems Quratulain Rajput

  15. According to Gruber and colleagues : • Definition: • “An ontology is a description (like a formal specification of a program) of the concepts and relationships that can exist for an agent or a community of agents.” • The above definition is consistent with the usage of ontology as use in philosophy in general but used in different sense in computer science. • Purpose: • designing ontologies for the purpose of enabling knowledge sharing and reuse • Use • build agents that commit to ontologies. design ontologies so we can share knowledge with and among these agents. • Ontological commitments are agreements to use the shared vocabulary in a coherent and consistent manner. Quratulain Rajput

  16. Ontology • Regardless of language common component of ontology includes: • Classes • Attributes • Relation • Restriction • Rules • Thus, we can say RDFS is a language to describe an ontology. Quratulain Rajput

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