1. Knowledge Representation and Inference
CS 480/580
Fall 2009

2. Requirements for Knowledge Representation Languages
Well-defined syntax and semantics
General requirements:
Representational adequacy
Inferential adequacy
Inferential efficiency
Clear syntax and semantics
Naturalness

3. Semantic Networks
Originally developed in 1960s to represent the meaning of English words

4. Frames Frames are a variant of semantic networks
Widely used in expert systems
Semantic networks and frames are interchangeable
Defaults and multiple inheritance
Slots and procedures

5. Predicate Logic This is the most important knowledge representation
Syntax:
P V Q
P ^ Q ¬Q
P → Q
P ↔ Q
P ^ (Q → R); (Q V ¬R) → P

6. Predicate Logic (cont.)
Notation: Begin with lower case letters for constants; Begin with a capital letter for variables; fatherof(allison, richard)
Prolog uses , : and ;: OR
More on Prolog …

7. Rule-based Systems If – then rules and facts Forward chaining system
Conflict resolution
Backward chaining system