Expert systems

1
Expert systems

• Subset of KBS machines
• production rule based
• commercial application
• DENDRAL
• mass spectrometry
• MACSYMA
• mathematics
• MYCIN (probably most famous)
• treatment of infectious diseases
• PROSPECTOR
• mineral exploration
• 100s of others
• agriculture
• chemistry
• computer systems
• electronics
• engineering

2
The nature of knowledge

• What is knowledge?
• what is known
• information vs. knowledge
• info. that can be expressed
• human knowledge
• Expressing knowledge
• when should you cry?
• how do you recognise a friend?
• what is a good film?
• can be discussed but not specified
• Using natural language
• much knowledge is expressed in English
• KBS use knowledge that can be written
• why not just use English then?

3
Nature of knowledge cont.

• Problems with using language
• storage efficiency
• a table of figures
• processing efficiency
• a story containing facts
• accuracy
• the kettle is boiling
• Ich bin ein Berliner
• computers cannot understand it
• Alternative (monotonic) formalisms
• formal logic
• propositional logic
• predicate logic
• production rules

4
Monotonic formalisms

• complete knowledge of domain
• consistency
• new facts don't contradict old rules
• Formal logic
• a precise and inflexible language
• concepts are represented by symbols
• formulae of symbols can be used to
• state logical conditions
• formulae contain operators
• e.g. AND ( ? )
• OR ( )
• NOT ( ? )
• context free
• e.g. using a die, if.
• A the event of throwing a 6
• B the event of throwing a 5
• C the event of throwing gt 4
• D the event of throwing lt 6

5
Monotonic formalisms

• Propositional logic
• Daisy(cow) ? cow(ruminant) ? Daisy(ruminant)
• cat(feline) ? feline(animal) ? cat(animal)
• (a,b) ? (b,c) ? (a,c)
• If an entitya is an entityb and entityb is an
  entityc then the entitya is also an entityc
• purely syntactic
• well formed formulae (wffs)
• manipulation of wffs
• form consequences

6
Monotonic formalisms

• Procedural knowledge
• no connection with inferred class inclusion
  (predicates)
• specify action in unpredictable states
• conditional logic
• IF car in first gear AND speed gt 10mph THEN
• select second gear
• ELSE
• stay in first gear
• END IF
• nonmonotonic to the extent that appropriate
  action is context sensitive
• action takes place according to actual
  circumstance
• Context sensitivity

7
Monotonic formalisms

• Predicate logic.
• includes concept of sets
• Existential quantifiers
• ? - there exists a set
• ? - all
• (( Cow, x) ? ( Ruminant, y) ? (" x, y))
• ( x, Daisy) ? (Daisy x, Ruminant)
• If there exists a set of things called cow and a
  set of things called ruminant and all cows are
  ruminants. Of the set cow, there exists a member
  called Daisy. Then Daisy is a ruminant.
• NB. e.g. precludes difficulties with little white
  flowers with yellow middles
• Make predictions