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Overview prolog

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Harry Potter

Prolog is a logic programming language well-suited for problems involving structured objects and relations. The document discusses how Prolog represents relations through facts and rules. Facts unconditionally declare true instances of a relation, like "parent(tom, bob)". Rules specify relations that are true if certain conditions hold, written as "head :- body". For example, the offspring relation is defined by the rule "offspring(Y, X) :- parent(X, Y)". Questions can then be asked and answered based on the defined facts and rules.

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An Overview of Prolog 1
What is Prolog  Prolog is a powerful language for AI and non- numerical programming  Stands for programming in logic  Centered around a small set of basic mechanisms, including:  Pattern matching  Tree-based data structuring  Automatic back tracking  Well suited for problems that involves structured objects and relations between them. 2
Chapter One: Introduction to Prolog 1. Defining relations by facts 2. Defining relations by rules 3. Recursive rules 4. How Prolog answers questions 5. Declarative and procedural meaning of programs 3
Chapter one: 1. Defining relations by facts 2. Defining relations by rules 4
1.1 Defining relations by facts 5 Example The fact that tom is a parent of bob parent(tom, bob). the name of a relation argument1 argument2 Fact clause
1.1 Defining relations by facts 6  The family tree is defined by the following Prolog program: parent(pam, bob) parent(tom, bob) parent(tom, liz) parent(bob, ann) parent(bob, pat) parent(pat, jim) This program consists of six clauses.  Each clause declares one fact about parent relation (particular instance of the parent relation) * a relation is the set of all its instances
1.1 Defining relations by facts 7 When the program communicated to Prolog system, Prolog can be posed some questions about the parent relation: Is bob a parent of pat? ?- parent(bob, pat) Prolog answer: True ?- parent(liz, pat) Prolog answer: No solutions ?- parent(tom, pat) Prolog answer: No solutions tom bob ann pat jim liz pam
1.1 Defining relations by facts 8 Who is liz’s parent? ?- parent(X, liz) Prolog answer: X = tom Who are bob’s children? ?- parent(bob, X) Prolog answer: X = ann. X = pat. tom bob ann pat jim liz pam
1.1 Defining relations by facts 9 Find X and Y such that X is a parent of Y. ?- parent (X, Y). Prolog answers: X = pam. Y = bob. X = tom. Y = bob. X = tom. Y = liz. X = bob. Y = ann. X = bob. Y = pat. X = pat. Y = jim. tom bob ann pat jim liz pam
1.1 Defining relations by facts 10 Who is a grandparent of jim? Who is the parent of jim? Assume that this is Y Who is the parent of Y? Assume that this is X ?- parent(Y, jim), parent (X, Y) Prolog answer: X = bob Y = pat • Changing the order of the requirements will affect the result. ?- parent(X, jim), parent (Y, X) Prolog answer: X = pat. Y = bob. ?- parent(X, jim), parent (X, Y) Prolog answer: X = pat. Y = jim. √ x x
1.1 Defining relations by facts 11 Do ann and pat have a common parent? Who is a parent X of ann? Is X a parent of pat? ?- parent (X, ann), parent(X, pat) Prolog answer: X = bob tom bob ann pat jim liz pam
1.2 Defining relations by rules 12  We can add the information on the sex of the people that occur in the parent relation: female(pam). male(tom). male(bob). female(liz). female(pat). female(ann). male(jim). male and female are unary relations, whereas parent is a binary relation. Gender(pam, female). Gender(tom, male). Gender(bob, male). tom bob ann pat jim liz pam
1.2 Defining relations by rules 13 Let us introduce the offspring relation (inverse of parent) offspring(liz, tom). offspring(bob, tom). ... The logical statement is: For all X and Y, Y is an offspring of X if X is a parent of Y offspring(Y, X) :- parent(X, Y). Rule clause tom bob ann pat jim liz pam Fact caluses
1.2 Defining relations by rules 14 There is an important difference between facts and rules:  Facts is something that is always, unconditionally, true parent(tom, liz).  Rules specify things that are true if some condition is satisfied. Rules have:  Condition part (right-hand side) = body  Conclusion part (left-hand side) = head offspring(Y, X) :- parent(X, Y). head body
1.2 Defining relations by rules 15 Questions  Is liz an offspring of tom? ?- offspring(liz, tom). Prolog answer: True How Prolog answer this question using the rule: Offspring(Y, X) :- parent(X, Y). Prolog answer: True
1.2 Defining relations by rules 16  How to express:  Mother relation  Grandparent relation  Sister relation in Prolog?
Important Points 17

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Overview prolog

  • 1. An Overview of Prolog 1
  • 2. What is Prolog  Prolog is a powerful language for AI and non- numerical programming  Stands for programming in logic  Centered around a small set of basic mechanisms, including:  Pattern matching  Tree-based data structuring  Automatic back tracking  Well suited for problems that involves structured objects and relations between them. 2
  • 3. Chapter One: Introduction to Prolog 1. Defining relations by facts 2. Defining relations by rules 3. Recursive rules 4. How Prolog answers questions 5. Declarative and procedural meaning of programs 3
  • 4. Chapter one: 1. Defining relations by facts 2. Defining relations by rules 4
  • 5. 1.1 Defining relations by facts 5 Example The fact that tom is a parent of bob parent(tom, bob). the name of a relation argument1 argument2 Fact clause
  • 6. 1.1 Defining relations by facts 6  The family tree is defined by the following Prolog program: parent(pam, bob) parent(tom, bob) parent(tom, liz) parent(bob, ann) parent(bob, pat) parent(pat, jim) This program consists of six clauses.  Each clause declares one fact about parent relation (particular instance of the parent relation) * a relation is the set of all its instances
  • 7. 1.1 Defining relations by facts 7 When the program communicated to Prolog system, Prolog can be posed some questions about the parent relation: Is bob a parent of pat? ?- parent(bob, pat) Prolog answer: True ?- parent(liz, pat) Prolog answer: No solutions ?- parent(tom, pat) Prolog answer: No solutions tom bob ann pat jim liz pam
  • 8. 1.1 Defining relations by facts 8 Who is liz’s parent? ?- parent(X, liz) Prolog answer: X = tom Who are bob’s children? ?- parent(bob, X) Prolog answer: X = ann. X = pat. tom bob ann pat jim liz pam
  • 9. 1.1 Defining relations by facts 9 Find X and Y such that X is a parent of Y. ?- parent (X, Y). Prolog answers: X = pam. Y = bob. X = tom. Y = bob. X = tom. Y = liz. X = bob. Y = ann. X = bob. Y = pat. X = pat. Y = jim. tom bob ann pat jim liz pam
  • 10. 1.1 Defining relations by facts 10 Who is a grandparent of jim? Who is the parent of jim? Assume that this is Y Who is the parent of Y? Assume that this is X ?- parent(Y, jim), parent (X, Y) Prolog answer: X = bob Y = pat • Changing the order of the requirements will affect the result. ?- parent(X, jim), parent (Y, X) Prolog answer: X = pat. Y = bob. ?- parent(X, jim), parent (X, Y) Prolog answer: X = pat. Y = jim. √ x x
  • 11. 1.1 Defining relations by facts 11 Do ann and pat have a common parent? Who is a parent X of ann? Is X a parent of pat? ?- parent (X, ann), parent(X, pat) Prolog answer: X = bob tom bob ann pat jim liz pam
  • 12. 1.2 Defining relations by rules 12  We can add the information on the sex of the people that occur in the parent relation: female(pam). male(tom). male(bob). female(liz). female(pat). female(ann). male(jim). male and female are unary relations, whereas parent is a binary relation. Gender(pam, female). Gender(tom, male). Gender(bob, male). tom bob ann pat jim liz pam
  • 13. 1.2 Defining relations by rules 13 Let us introduce the offspring relation (inverse of parent) offspring(liz, tom). offspring(bob, tom). ... The logical statement is: For all X and Y, Y is an offspring of X if X is a parent of Y offspring(Y, X) :- parent(X, Y). Rule clause tom bob ann pat jim liz pam Fact caluses
  • 14. 1.2 Defining relations by rules 14 There is an important difference between facts and rules:  Facts is something that is always, unconditionally, true parent(tom, liz).  Rules specify things that are true if some condition is satisfied. Rules have:  Condition part (right-hand side) = body  Conclusion part (left-hand side) = head offspring(Y, X) :- parent(X, Y). head body
  • 15. 1.2 Defining relations by rules 15 Questions  Is liz an offspring of tom? ?- offspring(liz, tom). Prolog answer: True How Prolog answer this question using the rule: Offspring(Y, X) :- parent(X, Y). Prolog answer: True
  • 16. 1.2 Defining relations by rules 16  How to express:  Mother relation  Grandparent relation  Sister relation in Prolog?

Editor's Notes

  1. offspring(bob, pam). offspring(ann, bob). offspring(pat, bob). offspring(jim, pat).