Building Knowledge Bases

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Building Knowledge Bases

• Lecture 7-1
• February 16th, 1999
• CS250

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What do we get from logic?

• Logics consist of
• Syntax
• Semantics
• Proof theory
• Expressive, but doesnt say what to express

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A Few Terms

• Knowledge engineering - Art science of
  transforming worldly knowledge into computer
  reasonable form
• Knowledge acquisition - Squeezing knowledge from
  the heads of experts

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Declarative Approach Rides Again

• Write down what you know, and let the system
  figure out the rest
• Separate inferencing from representation
• Design an inferencing engine that works with many
  representations
• Free to focus on the best representation

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Good Qualities for a Knowledge Base

• Clarity
• Coherence
• Extensibility
• Avoid favoring encodings
• Minimal ontological commitment
• From Toward Principles for the Deisgn of
  Ontologies Used for Knowledge Sharing

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KE Questions

• For every sentence added to the knowledge base
• Why is this true? Can its truth be decomposed?
• Is it widely applicable? Can I broaden this
  observation?
• Do I need a predicate to denote this class of
  objects? How does the class relate to other
  classes? Subclasses? Other class properties?

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KE Strategy

• Decide what to talk about
• What to focus on, what to ignore
• Vocabulary of predicates, functions constants
• Encode general domain knowledge
• Encode a specific problem instance
• Sit back and ask questions

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1-Bit Adder
1
1
2
3
2
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What are We Talking About

• Some concepts well need
• Wires as connectors
• Gates (AND, OR, XOR NOT)
• Inputs
• Outputs
• What dont we need?

Latency, layout, CMOS, time
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Representing Stuff

• Distinguish gates from one another
• Constants
• Gate types
• Type functions gt Type(X1) XOR
• Terminals
• Output terminal function Out(1, X1)
• Connectivity

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Encode General Rules

• If two terminals are connected, they have the
  same signal
• The signal at every terminal is either on or off
  (but not both)
• An XOR gate is on iff its inputs are different

?t1,t2 Connected(t1,t2)? Signal(t1)Signal(t2)
?t Signal(t)On ? Signal(t)Off On?Off
?g Type(g)XOR? Signal(Out(1,g)On ?
Signal(In(1,g))?Signal(In(2,g))
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Encode Specific Instance

• Encode the circuit
• Gate info
• Connections among gates

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Ask the 64,000 Question

• When will the first output of C1 be off and the
  second output of C1 to be on?
• Is the circuit correct?
• What are the possible sets of values of all the
  terminals for the adder circuit?

?i1,i2,o1,o2 Signal(In(1,C1))i1 ?
Signal(In(2,C1))i2 ? Signal(In(3,C1))i3 ?
Signal(Out(1,C1))o1 ? Signal(Out(2,C1))o2
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Other KRs

• Case-based reasoning
• Bayesian networks
• Neural networks

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General Ontologies

• Categories
• Measures
• Composite Objects
• Time, Space and Change
• Events and Processes
• Physical Objects
• Substances
• Mental Objects and Beliefs

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Categories

• Categories
• Reification
• How many people live on Earth?
• Inheritance
• Creating taxonomies
• Kentucky Fried Chicken
• Dewey decimal
• LoC
• MeSh

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Measures

• Examples Height, mass, cost
• Measure Units function a Number

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Composite Objects

• Not inheritance
• Difference between subclass and member
• Schema
• Script