Artificial Intelligence Expert Systems Prolog

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Artificial Intelligence / Expert SystemsProlog

• Justin Gaudry
• June 8, 2007

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Prolog

• PROgramming in LOGic
• First developed in 1975 to facilitate
  natural-language processing
• Based on relationships and logical inference

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Declarative Paradigm

• Does not describe how to compute a solution
• Program consists of a database
• Facts
• Logical rules
• Rules describe relationships for current
  application
• Building with blueprints not bricks

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Declarative Paradigm

• User does not run a program to obtain a solution
• A database is loaded into Prolog interpreter
• User asks a question
• Inference engine determines the answer by logical
  deduction

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Features

• Logical variables
• Behave like mathematical variables
• Unification
• Backtracking
• Uniform data structures
• Predicates and lists

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• Facts
• dog(fido).
• worksFor(hal, mary).
• Rules
• dog(X) - barks(X).
• worksFor(X,Y) - getsCoffee(Y,X).
• Queries (user questions)

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Elements of Prolog

• Variables
• Must begin with uppercase
• Weakly typed
• Constants
• Numbers
• Items starting with lowercase
• Items enclosed in single quotes ( )

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Simple Data Types

• boolean
• true, fail
• integer
• Integers
• real
• Floating point numbers
• variable
• Variables
• atom
• Character sequences

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Builtin Predicates

• var(V)
• V is a variable
• nonvar(NV)
• NV is not a variable
• atom(A)
• A is an atom
• integer(I)
• I is an integer
• real(R)
• R is a floating point number
• number(N)
• N is an integer or real
• atomic(A)
• A is an atom or a number

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Operators

• is assignment
• addition
• - subtraction
• multiplication
• / real division
• // integer division
• mod modulus
• power

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Command-Line Interface

• On osprey, sicstus
• Queries end with . (no quotes)
• file. Loads the file from current directory
• halt. Exits sicstus

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Recursion

• Basic control structure
• Inductive definitions
• Base case(s)
• Inductive case(s)