fr.boreal.backward_chaining.cover.QueryCover Maven / Gradle / Ivy
package fr.boreal.backward_chaining.cover;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import fr.boreal.backward_chaining.homomorphism.QueryHomomorphism;
import fr.boreal.model.formula.api.FOFormula;
import fr.boreal.model.query.api.FOQuery;
import fr.boreal.model.ruleCompilation.NoRuleCompilation;
import fr.boreal.model.ruleCompilation.api.RuleCompilation;
/**
* Computes the cover of a set of queries using homomorphism to detect if a query is more general than another
*/
public class QueryCover implements CoverFunction {
private final QueryHomomorphism queryHomomorphism;
/**
* Default constructor.
* Uses no compilation
*/
public QueryCover() {
this(NoRuleCompilation.instance());
}
/**
* Constructor with compilation
* @param compilation the compilation to use
*/
public QueryCover(RuleCompilation compilation) {
this.queryHomomorphism = new QueryHomomorphism(compilation);
}
@Override
public Set> cover(Set> queries) {
Set> cover = new HashSet<>();
for(FOQuery q1 : queries) {
boolean toAdd = true;
Iterator> coverIt = cover.iterator();
while (coverIt.hasNext()) {
FOQuery q2 = coverIt.next();
if(this.isMoreGeneralThan(q2, q1)) {
toAdd = false;
break;
}
else if(this.isMoreGeneralThan(q1, q2)) {
coverIt.remove();
}
}
if(toAdd) {
cover.add(q1);
}
}
return cover;
}
/**
* @return true iff q1 subsumes q2
*/
private boolean isMoreGeneralThan(FOQuery q1, FOQuery q2) {
return this.queryHomomorphism.exists(q1, q2);
}
}