2 Knowledge Representation

The Meaning of Knowledge

• Data
• Information
• Knowledge

Productions

• Syntax defined by BNF(Backus-Naur Form)
• All sentences can be generated by successively replacing each non-terminal by its RHS non-terminals or terminals until all non-terminals are eliminated.

Grammar

    G = (VN, VT, P, S)
        V: vocabulary
        N: non-terminals
        T: terminals
        P: productions
        S: the starting symbol

Grammar Types

1. Recursively Enumerable Language
2. Context-Sensitive Language

               u X v => u Y v
   
              X : single non-terminal
              Y : non-empty string
           u, v : arbitrary string
   

   Example:

       S => aSBC
       S => aBC
       CB => BC    S : Starting symbol
       aB => ab    A, B, C : non-terminals
       bB => bb    a, b, c : terminals
       bC => bc
       cC => cc
   

3. Context-Free Language
   LHS must contain only a single non-terminal
4. Regular Language(Finite-state Grammar)

Semantic Nets

1. Nodes -- Objects
2. Arc (Links or Edges) -- relations

       ISA   : is an instance of
       AKO   : is a subclass of
       HAS-A
   

Object-Attribute-Value Triplets

Prolog

Frames

Scripts

Logic

1. Propositional Logic
2. First Order Predicate Logic