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Understanding Knowledge Representation in First-Order Logic and Semantic Networks

This supplemental content for CSE 327 by Prof. Jeff Heflin explores knowledge representation through categories in First-Order Logic (FOL) and Semantic Networks. It discusses unary predicates, inheritance, and reified categories, demonstrating how objects like laptops and birds are categorized and their relationships defined. Examples of classification and subsumption illustrate essential inference tasks. The slides also touch on nonmonotonic logic, where new information can change prior beliefs, using engaging examples like birds and their flying capabilities.

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Understanding Knowledge Representation in First-Order Logic and Semantic Networks

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  1. Ch. 12 – Knowledge Representation Supplemental slides for CSE 327 Prof. Jeff Heflin

  2. Categories in FOL • unary predicate representation Laptop(DellD600) • x Laptop(x)  Computer(x) • x Computer(x)  Electronic(x) • reified category representation • Member(DellD600, Laptop) • Subset(Laptop, Computer) • Subset(Computer, Electronic) • x,y,z Subset(x,y)  Subset(y,z)  Subset(x,z) • x,y,z Member(x,y)  Subset(y,z)  Member(x,z)

  3. Semantic Networks • a kind of logic that uses a graphical notation • graph with labeled nodes and arcs • nodes represent categories and individual objects • arcs represent relations between objects Granny cage12 owner livesIn Tweety

  4. Inheritance in Semantic Nets • The properties of a category can be inherited by their members • Drawn with a single box canFly Bird True MemberOf Implies that canFly for Tweety is true Tweety

  5. Overriding Inheritance canFly • Values of class relations are defaults • e.g. some birds cannot fly • Nonmonotonic • New information can cause you to revoke prior conclusions • If we only know Opus is a Bird, but then later learn that he is a Penguin Bird True SubsetOf canFly Penguin False MemberOf Implies that canFly for Opus is false Opus

  6. Events in Semantic Networks FlyEvent Member Fly17 Agent During Shankar Yesterday Origin Destination NewYork NewDelhi From Fig. 10.10, p. 352

  7. Description Logic

  8. DL Inference Tasks • classification • does an object belong to a category? • example • bobMale, bobParent • is bobFather? • subsumption • is one category a subset of another? • given • Herbivore  And(Animal, All(eats, Plant)) • a herbivore is an animal that only eats plants • Giraffe  And(Animal, All(eats, Leaves)) • a giraffe is an animal that only eats leafs • Leaves  Plant • leaves are plants • is Giraffe  Herbivore true?

  9. Cyc Upper Ontology From http://www.cyc.com/cycdoc/vocab/upperont-diagram.html

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