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BackwardChaining.java
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BackwardChaining.java
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import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
/**
* Created by Frank on 10/28/14.
*/
public class BackwardChaining {
private String andOperator = "&";
private String implicationOperator = "=>";
private String variable = "x";
public static boolean isFact = false;
public String query;
public int numberOfClauses;
public List<String> knowledgeBase = new ArrayList<String>();
public static void main(String[] args) {
BackwardChaining bc = new BackwardChaining();
String x = "A(b,c)";
String y = "A(x,c)";
String theta = "";
String conclusion = bc.unify(x, y, theta);
System.out.println(conclusion);
}
public BackwardChaining() {
}
public BackwardChaining(String query, int numberOfClauses, List<String> knowledgeBase) {
this.query = query;
this.numberOfClauses = numberOfClauses;
this.knowledgeBase = knowledgeBase;
}
public boolean backwardChaining(List<Predicate> queries, List<String> knowledgeBase) {
Predicate conclusion = new Predicate();
// conclusion = queries.get(0);
boolean[] truthOfQueries = new boolean[queries.size()];
for (int i = 0; i < truthOfQueries.length; i++) {
truthOfQueries[i] = false;
}
boolean[] truthOfQueries2 = new boolean[queries.size()];
for (int i = 0; i < truthOfQueries2.length; i++) {
truthOfQueries2[i] = false;
}
int index = 0;
for (Predicate q : queries) {
conclusion = q;
for (String a : knowledgeBase) {
if (isAtomic(a) == false) {
Predicate conclusion2;
conclusion2 = parseGetConclusion(a);
if (conclusion.getPredicate().equals(conclusion2.getPredicate())) {
if (conclusion.getArgument1().equals(conclusion2.getArgument1())
|| conclusion.getArgument1().equals(this.variable)
|| conclusion2.getArgument1().equals(this.variable)) {
if (conclusion.getArgument2() == null) {
continue;
}
if (conclusion2.getArgument2() == null) {
continue;
}
if (conclusion.getArgument2().equals(conclusion2.getArgument2())
|| conclusion.getArgument2().equals(this.variable)
|| conclusion2.getArgument2().equals(this.variable)) {
//return true;
List<Predicate> conditions = parseGetPredicates(a);
for (int i = 0; i < conditions.size(); i++) {
conditions.get(i).println();
}
return backwardChaining(conditions, knowledgeBase);
//return parseGetPredicates(a)
}
}
}
} else {
Predicate conclusion2;
conclusion2 = parsePredicate(a);
if (conclusion.getPredicate().equals(conclusion2.getPredicate())) {
if (conclusion.getArgument2() != null && conclusion2.getArgument2() != null) {
if (conclusion.getArgument1().equals(conclusion2.getArgument1())
|| conclusion.getArgument1().equals(this.variable)
|| conclusion2.getArgument1().equals(this.variable)) {
if (conclusion.getArgument2().equals(conclusion2.getArgument2())
|| conclusion.getArgument2().equals(this.variable)
|| conclusion2.getArgument2().equals(this.variable)) {
//return true;
conclusion2.println();
truthOfQueries[index] = true;
break;
}
}
} else {
if (conclusion.getArgument1().equals(conclusion2.getArgument1())
|| conclusion.getArgument1().equals(this.variable)
|| conclusion2.getArgument1().equals(this.variable)) {
//return true;
conclusion2.println();
truthOfQueries[index] = true;
break;
}
}
}
}
}
index++;
}
for (int i = 0; i < truthOfQueries.length; i++) {
if (truthOfQueries[i] == false) {
return false;
}
}
return true;
}
/* public boolean fol_bc_ask(List<String> knowledgeBase, String query) {
return fol_bc_or(knowledgeBase, query, theta);
}
public boolean fol_bc_or(List<String> knowledgeBase, String goal, List<String> theta) {
for (String a: knowledgeBase) {
if (!isAtomic(a)) {
}
}
}
public boolean fol_bc_and(List<String> knowledgeBase, String goals, List<String> theta) {
if (theta == null) {
return false;
} else if (goals.length() == 0) {
return
}
}*/
public boolean fol_bc_ask(List<String> knowledgeBase, String query) {
List<String> result = fol_bc_or(knowledgeBase, query, "");
System.out.println(result.size());
for(String s: result)
System.out.println(s);
if (result.size() == 0) {
return false;
} else {
return true;
}
}
public List<String> fol_bc_or(List<String> knowledgeBase, String goal, String theta) {
List<String> matches = new ArrayList<String>();
List<String> or_unifications = new ArrayList<String>();
for (int i = 0; i < knowledgeBase.size(); i++) {
if (matches(parseGetConclusionString(knowledgeBase.get(i)), goal)) {
matches.add(knowledgeBase.get(i));
}
}
for (int i = 0; i < matches.size(); ++i) {
String line = matches.get(i);
if (isCompoundStatement(line)) {
isFact = false;
} else {
isFact = true;
}
String unifies = unify(parseGetConclusionString(line), goal,"");
List<String> unifications = fol_bc_and(knowledgeBase, parseGetPremises(line), unifies);
for (String s : unifications) {
if(!or_unifications.contains(s))
or_unifications.add(s);
}
}
return or_unifications;
}
public List<String> fol_bc_and(List<String> knowledgeBase, List<String> goals, String theta) {
List<String> unifications = new ArrayList<String>();
if (theta == null) {
return unifications;
} else if (goals == null || goals.size() == 0) {
if(!unifications.contains(theta))
unifications.add(theta);
return unifications;
} else {
String first = goals.get(0);
List<String> rest = new ArrayList<String>();
for (String goal : goals)
rest.add(goal);
rest.remove(0);
List<String> or_unifications = fol_bc_or(knowledgeBase, substitute(first, theta), theta);
for (String or_unifier : or_unifications) {
List<String> and_unifications = fol_bc_and(knowledgeBase, rest, or_unifier);
for (String and_unifier : and_unifications)
if(!unifications.contains(and_unifier))
unifications.add(and_unifier);
}
}
return unifications;
}
public String unify(String x, String y, String theta) {
if (hasVariable(y) == 1 && !isFact) {
return "";
} else if (x.equals(y)) {
return theta;
} else if (x.equals(this.variable)) {
return y;
} else if (y.equals(this.variable)) {
if(isFact)
return x;
else
return "";
} else if (isAtomic(x) && isAtomic(y)) {
Predicate predicate1 = parseGetConclusion(x);
Predicate predicate2 = parseGetConclusion(y);
if (predicate1.getArgument2() == null) {
predicate1.setArgument2("");
}
if (predicate2.getArgument2() == null) {
predicate2.setArgument2("");
}
return unify(predicate1.getArgument2(), predicate2.getArgument2(), unify(predicate1.getArgument1(), predicate2.getArgument1(), theta));
} else {
return null;
}
}
/* public boolean matches(String string1, String string2) {
Predicate predicate1 = parsePredicate(string1);
Predicate predicate2 = parsePredicate(string2);
if (predicate1.getPredicate().equals(predicate2.getPredicate())) {
return true;
} else {
return false;
}
}*/
public boolean matches(String string1, String string2) {
String stringA = string1.substring(0, string1.indexOf("("));
String stringB = string2.substring(0, string2.indexOf("("));
if (stringA.equals(stringB)) {
return true;
} else {
return false;
}
}
/*
public String unify_var(String var, String x, List<String> theta) {
if (theta.contains(var)) {
return unify(val, x, theta);
} else if (theta.contains(x)) {
return unify(var, val, theta);
} else {
theta.add(var);
return var;
}
}
public boolean backwardChaining(Predicate goal) {
}*/
public String substitute(String string, String theta) {
if (theta.equals("")) {
return string;
}
Predicate predicate = parsePredicate(string);
if (predicate.getArgument1().equals(this.variable)) {
predicate.setArgument1(theta);
} else if (predicate.getArgument2() != null) {
if (predicate.getArgument2().equals(this.variable)) {
predicate.setArgument2(theta);
}
} else {
return string;
}
StringBuilder builder = new StringBuilder();
builder.append(predicate.getPredicate());
builder.append('(');
builder.append(predicate.getArgument1());
if (predicate.getArgument2() != null) {
if (!predicate.getArgument2().equals("")) {
builder.append(',');
builder.append(predicate.getArgument2());
}
}
builder.append(')');
return builder.toString();
}
public int hasVariable(String input) {
if (isAtomic(input)) {
Predicate predicate = parsePredicate(input);
if (predicate.getArgument1() == this.variable) {
return 1;
}
if (predicate.getArgument2() == this.variable) {
return 1;
}
return 0;
}
return -1;
}
public List<Predicate> parseGetPredicates(String line) {
List<Predicate> predicates = new ArrayList<Predicate>();
List<String> string1 = new ArrayList<String>();
string1 = parseImplication(line);
String premises = string1.get(0);
//String conclusion = string1.get(1);
List<String> string2 = parseAnd(premises);
for (String s : string2) {
predicates.add(parsePredicate(s));
}
return predicates;
}
public List<String> parseGetPremises(String line) {
if (!line.contains(this.implicationOperator)) {
return null;
} else {
List<String> strings = parseImplication(line);
String leftHandSide = strings.get(0);
List<String> premises = parseAnd(leftHandSide);
return premises;
}
}
public Predicate parseGetConclusion(String line) {
List<String> string1 = parseImplication(line);
String conclusion;
if (!line.contains(this.implicationOperator)) {
conclusion = string1.get(0);
} else {
conclusion = string1.get(1);
}
Predicate q = parsePredicate(conclusion);
return q;
}
public String parseGetConclusionString(String line) {
List<String> strings = parseImplication(line);
if (line.contains(this.implicationOperator)) {
return strings.get(1);
} else {
return strings.get(0);
}
}
public boolean isAtomic(String line) {
if (line.contains(this.andOperator)) {
return false;
} else if (line.contains(this.implicationOperator)) {
return false;
} else {
if (line.contains("(")) {
return true;
} else {
return false;
}
}
}
public boolean isCompoundStatement(String input) {
if (input.contains(this.implicationOperator)) {
return true;
} else {
return false;
}
}
public List<String> parseImplication(String string) {
Scanner sc = new Scanner(string).useDelimiter(this.implicationOperator);
List<String> parts = new ArrayList<String>();
if (isAtomic(string)) {
parts.add(string);
return parts;
}
parts.add(sc.next());
parts.add(sc.next());
return parts;
}
/* public List<Predicate> parseAnd(String line) {
Scanner sc = new Scanner(line).useDelimiter(this.andOperator);
List<Predicate> predicates = new ArrayList<Predicate>();
while (sc.hasNext()) {
Predicate predicate = new Predicate();
predicate.setPredicate(sc.next());
predicates.add(predicate);
}
return predicates;
}*/
public List<String> parseAnd(String string) {
Scanner sc = new Scanner(string).useDelimiter(this.andOperator);
List<String> clauses = new ArrayList<String>();
while (sc.hasNext()) {
clauses.add(sc.next());
}
return clauses;
}
public Predicate parsePredicate(String string) {
Predicate predicate = new Predicate();
String argument1 = string.substring(string.indexOf("(") + 1, string.lastIndexOf(")"));
// System.out.println(argument1);
Scanner sc = new Scanner(argument1).useDelimiter(",");
List<String> arguments = new ArrayList<String>();
while (sc.hasNext()) {
arguments.add(sc.next().trim());
}
String predicateName = string.substring(0, string.indexOf("("));
// System.out.println(arguments);
predicate.setPredicate(predicateName);
predicate.setArgument1(arguments.get(0));
if (arguments.size() == 2) {
predicate.setArgument2(arguments.get(1));
}
return predicate;
}
}