CODEWITHSUNDEEP
javaartificial-intelligencefirst-order-logic
Hamza TAOURIRT
Hamza TAOURIRT

Reputation: 21

TweetyProject for first order logic

I'm trying to learn how to use coding for Logic Knowledge Representation and ultimately ML/AI.

I'm trying to make a java Tweety code about first order logic run but I always get the same error: the formula is not closed.

I know the meaning of a formula not being the in FOL, I just can't understand where the problem is in my code.

Here is the code:

public class SimpleFolExample {
    public static void main(String[] args) throws ParserException, IOException {
        // Create FOL signature
        FolSignature signature = new FolSignature(true);
     // Add sorts
     // Add sorts
        Sort sortPerson = new Sort("Person");
        signature.add(sortPerson);

        // Add constants
        Constant alice = new Constant("Alice", sortPerson);
        Constant bob = new Constant("Bob", sortPerson);
        Constant James = new Constant("James", sortPerson);
        signature.add(alice, bob, James);

        // Add predicates
     // Add predicates
        List<Sort> personPredicateSorts = new ArrayList<>();
        personPredicateSorts.add(sortPerson);
        Predicate person = new Predicate("Person", personPredicateSorts);
        signature.add(person); // Add predicates to the signature

        // Add the 'Knows' predicate (assuming it relates persons)
        List<Sort> knowsPredicateSorts = new ArrayList<>();
        knowsPredicateSorts.add(sortPerson);
        knowsPredicateSorts.add(sortPerson);
        Predicate knows = new Predicate("Knows", knowsPredicateSorts);
        signature.add(knows);
       

        // Display the signature
        System.out.println("Signature: " + signature);

        // Parse formulas using the signature
        FolParser parser = new FolParser();
        parser.setSignature(signature); // Set the FOL signature for the parser

        FolBeliefSet beliefSet = new FolBeliefSet();
        FolFormula f1 = (FolFormula) parser.parseFormula("Knows(Alice, Bob)");
        FolFormula f2 = (FolFormula) parser.parseFormula("Knows(Bob, James)");
        beliefSet.add(f1, f2);
    

        System.out.println("\nParsed Belief Base: " + beliefSet);

        // Use the reasoner to query the knowledge base
        FolReasoner.setDefaultReasoner(new SimpleFolReasoner());
        FolReasoner prover = FolReasoner.getDefaultReasoner();

        FolFormula query = (FolFormula) parser.parseFormula("exists X:(Knows(Alice, X))");


        System.out.println("Query: " + query + "\nResult: " + prover.query(beliefSet, query));
    }
    }

here is the error:

Signature: [_Any = {}, Person = {Bob, Alice, James}], [==(_Any,_Any), /==(_Any,_Any), Person(Person), Knows(Person,Person)], []

Parsed Belief Base: { Knows(Bob,James), Knows(Alice,Bob) }
Exception in thread "main" java.lang.IllegalArgumentException: The given formula exists X: (Knows(Alice,X)) is not closed.
    at org.tweetyproject.logics.fol.reasoner.SimpleFolReasoner.query(SimpleFolReasoner.java:45)
    at org.tweetyproject.logics.fol.examples.SimpleFolExample.main(SimpleFolExample.java:82

Upvotes: 2

Views: 103

Answers (1)

Olivier
Olivier

Reputation: 33

The problem can be solved if the constants are in lower case: alice, bob, james instead of Alice, Bob, James.

Upvotes: 0

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