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CHAPTER 2 The Representation of Knowledge

CHAPTER 2 The Representation of Knowledge. 2.3 PRODUCTIONS 2.4 SEMANTIC NETS BY chau nguyen. 2.3 PRODUCTIONS. Backus- Naurform (BNF) It is used to define the syntax of language.

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CHAPTER 2 The Representation of Knowledge

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  1. CHAPTER 2The Representationof Knowledge 2.3 PRODUCTIONS 2.4 SEMANTIC NETS BY chaunguyen

  2. 2.3 PRODUCTIONS Backus-Naurform (BNF) It is used to define the syntax of language. John Backus, a programming language designer at IBM, proposed "metalinguistic formulas" to describe the syntax of the new programming language IAL, known today as ALGOL 58 (1959), using the BNF notation. (http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form)

  3. 2.3 PRODUCTIONS • The BNF notation for English language rule that consists of a noun, a verb, by ending punctuation • Production Rule: • <sentence>::=<subject> <verb><end-mark> • The angle brackets, <> and ::= are symbols of the metalanguage. • ::= mean “is defined as” and is the BNF equivalent of the arrow • <sentence>-><subject><verb><end-mark> • The terms within the brackets are called nonterminal symbols or for short nonterminal

  4. 2.3 PRODUCTIONS A nonterminal is a variable A terminal is a variable but it cannot be replaced by anything else and so is a constant.

  5. 2.3 PRODUCTIONS • The bar mean “or” in the metalanguage: • <subject> -> I | You | We • <verb> -> left | came • <end-mark> -> . | ? | ! • The following are some productions:

  6. 2.3 PRODUCTIONS • A set of terminals is called a string of the language. • Example: • “We,” “WeWe,” and “leftcamecame” valid string but not valid sentences. • A grammar is a complete of production rules that define language unambiguously. • <sentence>-><subject><verb><object><end-mark> • <object> -> home | work | school

  7. 2.3 PRODUCTIONS <sentence> -> <subject phrases> <verb> <object phrase> <subject phrases> -> <determiner> <noun> <object phrases> -> <determiner> <adjective> <noun> <determiner> -> a | an | the | this | these | those <noun> -> man | eater <verb> -> is | was <adjective> -> dessert | heavy

  8. Parse Tree of a Sentence

  9. 2.3 PRODUCTIONS The man was a dessert eater. An eater was the heavy man.

  10. 2.4 SEMANTIC NETS • A semantic network, or net, is classic AI presentation technique used for propositional information. • A semantic net is also called a propositional net. • Proposition is a statement that either true or false. • Example: • “all dog are mammals” • “a triangle has three sides” • A proposition is always true or false and is called atomic because true value no further divided.

  11. 2.4 SEMATIC NETS The structure of a semantic net is shown graphically in term of nodes and the arcs connecting them. Nodes are sometimes referred to as object and arcs as links or edges. Links or edges of semantic net are used to express relationship.

  12. 2.4 Semantic Net

  13. 2.4 SEMANTIC NETS Without relationship, knowledge is simply a collection of unrelated facts.

  14. 2.4 Semantic Net

  15. 2.4 SEMANTIC NETS IS-A A-Kind-Of (AKO)

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