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Lecture 10: Semantic Network

Lecture 10: Semantic Network. Concepts Relations FOL. Heshaam Faili hfaili@ece.ut.ac.ir University of Tehran. Semantic Networks. A Semantic Network (SN) is a simple notation scheme for logical knowledge representation. A SN consists of a concepts and relations between concepts.

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Lecture 10: Semantic Network

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  1. Lecture 10: Semantic Network Concepts Relations FOL Heshaam Faili hfaili@ece.ut.ac.ir University of Tehran

  2. Semantic Networks • A Semantic Network (SN) is a simple notation scheme for logical knowledge representation. • A SN consists of a conceptsand relations between concepts. • Representing a SN with a directed graph : • Vertices : denote concepts. • Edges : represent relation between concepts. • The graphical depiction associated with a SN is a significant reason for their popularity.

  3. Taller than Bill John Bill John height height Greater than 180 h1 h2 value Semantic NetworksExample (1) • “Bill is taller than John .” • Non appropriate scheme : • Appropriate scheme :

  4. height height Taller than Greater than h1 h2 Semantic NetworksRelations • For an appropriate scheme: • Draw relations on the basic of primitives. • Represent complicated relations with this primitives. Basic primitive

  5. Semantic NetworksRelations • The ISA (is-a) relation is often used to link instances to classes, classes to superclasses. • Some links (e.g. isPart) are inherited along ISA paths. • The semantics of a SN can be relatively very formal or informal. • often defined at the implementation level

  6. furniture is - a isPart Chairs Seat is - a owner color Me My chair Tan is - a is - a covering Brown Person Leather Semantic NetworksRelations

  7. Eagle is - a is - a Birds Animal is - a Travel by Panguin Travel by Fly Walk Semantic NetworksRelations • Some times we had to override a relation for an inherited node (e.g travel by).

  8. Semantic NetworksReification • Non-binary relationships can be represented by “turning the relationship into an object” • This is an example of what logicians call “reification”. • consider an abstract concept to be real. • We might want to represent the generic give event as a relation involving four things: an agent, a recipient, an object and an activation time.

  9. Time is - a Past Gave Verb Recipient Object Agent Mary John The book Semantic NetworksReification • Consider this : “John gave Mary the book.” • Abstract concept (gave) => real.

  10. Semantic NetworksExample (2) • Family relationships. • Primitives : • father, mother, brother, sister, son, daughter. • More complicated relations representing with primitives: • aunt ( man ) : sister ( father ( man )) • causion ( man ) : son ( brother ( mother ( man ))) • etc .

  11. Semantic NetworksExample (3) • “Every dogs has bitten a postman.” • Is equal to : • X ( dog(X) Y ( postman(Y) & bitten(X, Y))) • Represent SN for one (dog, postman). • Quantify the represented SN. • GS is the set of generilized statements that has been quanified.

  12. Dog Bit Postman is - a is - a is - a Agent Object GS d b p is - a  g Form Semantic NetworksExample (3)

  13. ?

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