Bratko, Chapter 14: Expert Systems and Knowledge Representation

14.1 Functions of an Expert System
- problem solving
  - using domain-specific knowledge
  - dealing with uncertainty
- user interaction
  - explanation of intentions and decisions

14.2 Main Structure of an Expert System
- knowledge base
- inference engine } These two comprise an expert
- user interface   } system shell or shell

14.3 Representing Knowledge with If-Then Rules
- also called production rules
- properties of if-then rules
  - modular
  - incremental
  - modifiable
  - transparent
    - support 'how did you reach this conclusion' questions
    - support 'why are you interested in this information' questions
- can add certainty to rules
- can add necessity and sufficiency of conditions for conclusions

14.4 Forward and Backward Chaining in Rule-Based Systems
- backward chaining
  - Prolog already does backward chaining
  - better rule/fact interface [fig14.6, p339]
    - is_true(Fact), if Condition then Conclusion
- forward chaining [fig14.7, p341]
  - assert facts as derived

14.5 Generating Explanation
- 'how', ie, proof tree [fig14.8, p344]
- 'why', see Chapter 15

14.6 Introducing Uncertainty
- representation
  - Proposition : Certainty
  - if Condition then Conclusion : Certainty
- simple combination strategy
  - c(P1 and P2) = min(c(P1),c(P2))
  - c(P1 or P2) = max(c(P1),c(P2))
  - if P1 then P2 : C, c(P2) = c(P1) * C
- interpreter with uncertainties [fig14.9, p346]
  - colon already an operator (package)
  - have to prove all disjuncts of an OR

14.7 Difficulties in Handling Uncertainty
- assumption of independence
  - if a and b then c, a and b may correlate
- belief networks help [later, RN]

14.8 Semantic Networks and Frames
- semantic networks
  - isa(Class1,Class2), isa(Instance,Class)
  - Property(Class,Value), Property(Instance,Value)
  - inheritance
    - fact(Fact) :- Fact, !.
    - fact(Fact) :-
        Fact =.. [Rel,Arg1,Arg2],
        isa(Arg1,SuperArg),
        SuperFact =.. [Rel,SuperArg,Arg2],
        fact(SuperFact).
- frames
  - a frame consists of a set of filled/unfilled slots
    - properies, a_kind_of, instance_of
  - unfilled slots filled using inheritance
  - procedural slot
    - define procedure
    - pass instance reference up through hierarchy until procedure
      call found