org.aksw.jena_sparql_api.utils.CnfUtils Maven / Gradle / Ivy
package org.aksw.jena_sparql_api.utils;
import java.util.AbstractMap.SimpleEntry;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import org.apache.jena.graph.Node;
import org.apache.jena.query.Query;
import org.apache.jena.query.QueryFactory;
import org.apache.jena.sparql.algebra.Algebra;
import org.apache.jena.sparql.algebra.Op;
import org.apache.jena.sparql.core.Var;
import org.apache.jena.sparql.expr.E_Equals;
import org.apache.jena.sparql.expr.E_LogicalAnd;
import org.apache.jena.sparql.expr.E_LogicalNot;
import org.apache.jena.sparql.expr.E_LogicalOr;
import org.apache.jena.sparql.expr.E_NotEquals;
import org.apache.jena.sparql.expr.Expr;
import org.apache.jena.sparql.expr.ExprFunction;
import org.apache.jena.sparql.expr.ExprFunction2;
import org.apache.jena.sparql.expr.ExprList;
import org.apache.jena.sparql.expr.NodeValue;
// TODO There is already org.apache.jena.sparql.algebra.optimize.TransformFilterConjunction
public class CnfUtils {
@SuppressWarnings("unchecked")
public static T normalize(T expr) {
Expr a = expr.getArg1();
Expr b = expr.getArg2();
Expr result = a.isConstant() && b.isVariable()
? expr.copy(b, a)
: expr
;
return (T)result;
}
public static Entry extractEquality(Set clause) {
Entry result = null;
if(clause.size() == 1) {
Expr expr = clause.iterator().next();
if(expr instanceof E_Equals) {
E_Equals eq = (E_Equals)expr;
eq = normalize(eq);
Expr a = eq.getArg1();
Expr b = eq.getArg2();
if(a.isVariable() && b.isConstant()) {
Var v = a.asVar();
Node c = b.getConstant().getNode();
result = new SimpleEntry<>(v, c);
}
}
}
return result;
}
/**
* Extract from the CNF all mappings from a variable to constant, i.e.
* if there is ?x = foo, then the result will contain the mapping ?x -> foo.
*
*
* @param cnf
* @return
*/
public static Map getConstants(Iterable> cnf) {
Map result = new HashMap();
for(Set clause : cnf) {
Entry entry = extractEquality(clause);
if(entry != null) {
Var v = entry.getKey();
Node c = entry.getValue();
Node o = result.get(v);
if(o != null && !o.equals(c)) {
c = NodeValue.FALSE.getNode();
}
result.put(v, c);
}
}
return result;
}
public static Expr toExpr(Iterable> cnf) {
ExprList exprList = toExprList(cnf);
Expr result = ExprUtils.andifyBalanced(exprList);
return result;
}
public static ExprList toExprList(Iterable> cnf) {
ExprList result = new ExprList();
for(Set clause : cnf) {
if(!clause.equals(ClauseUtils.TRUE)) {
Expr expr = ExprUtils.orifyBalanced(clause);
result.add(expr);
}
}
return result;
}
public static void main(String[] args)
{
//!a->b&(a|d&b)
String sA = "Select * { ?s ?p ?o . Filter((!(!?a) || ?b) && (?a || ?d && ?b)) . }";
//String sA = "Select * { ?s ?p ?o . Filter(?o != ). Optional { { ?x ?y ?z . Filter(?x != && ?x = ?y) . } Union { ?x a ?y . Filter(?x = ) . } } . }";
//String sA = "Select * { ?s ?p ?o . Filter(!(?s = ?p || ?p = ?o && ?s = ?o || ?o = ?s)) . }";
//String sA = "Select * { ?s ?p ?o . Filter(!(?s = ?p || ?j = )) . }";
Query qA = QueryFactory.create(sA);
Op opA = Algebra.compile(qA);
opA = Algebra.toQuadForm(opA);
//System.out.println(opA);
// How to deal with union? variables appearing in them
//System.out.println(opA.getClass());
ExprList exprs = FilterUtils.collectExprs(opA, new ExprList());
Expr expr = ExprUtils.andifyBalanced(exprs);
Expr x = eval(expr);
System.out.println("HERE: " + x);
Set> cnf = toSetCnf(expr);
System.out.println("THERE: " + cnf);
/*
ExprList proc = eval(exprs);
System.out.println(proc);
List clauses = dnfToClauses(proc);
System.out.println("Mentioned vars:" + proc.getVarsMentioned());
System.out.println("Clauses: " + clauses);
*/
}
/**
* Test if the candidate is subsumed by the reference.
* This means that the candidate must contain at least all constraints of ref
*
* @param cand
* @param ref
* @return
*/
public static boolean isSubsumedBy(Set> cand, Set> ref) {
boolean result = true;
for(Set clause : ref) {
boolean isContained = cand.contains(clause);
if(!isContained) {
result = false;
break;
}
}
return result;
}
/**
* Return a sub cnf that where each element of a clause contains all variables
*
* @param clauses
* @param requiredVars
* @return
*/
/*
public static Set> filterByVars(Set> clauses, Set requiredVars) {
Set> result = new HashSet>();
for(Set clause : clauses) {
Set tmp = null;
for(Expr expr : clause) {
if(!expr.getVarsMentioned().containsAll(requiredVars)) {
continue;
}
if(tmp == null) {
tmp = new HashSet();
}
tmp.add(expr);
}
if(tmp != null) {
result.add(tmp);
}
}
return result;
}
*/
public static Set> toSetCnf(ExprList exprs)
{
List clauses = toClauses(exprs);
Set> cnf = FilterUtils.toSets(clauses);
return cnf;
}
public static Set> toSetCnf(Expr expr)
{
Set> result;
if(NodeValue.TRUE.equals(expr)) {
result = new HashSet<>(); // Return a new set, as callers may want to extend the set//Collections.emptySet();
} else {
List clauses = toClauses(expr);
result = FilterUtils.toSets(clauses);
}
return result;
}
public static List toClauses(Expr expr)
{
Expr evaluated = eval(expr);
return evaluated == null ? null : cnfToClauses(Collections.singleton(evaluated));
}
public static List toClauses(ExprList exprs)
{
Expr evaluated = eval(ExprUtils.andifyBalanced(exprs));
return evaluated == null ? null : cnfToClauses(Collections.singleton(evaluated));
}
/**
* This method only words if the input expressions are in DNF,
* otherwise you will likely get junk back.
*
* @param exprs
* @return
*/
public static List cnfToClauses(Iterable exprs) {
List result = new ArrayList();
for(Expr expr : exprs) {
collectAnd(expr, result);
}
return result;
}
public static void collectAnd(Expr expr, List list)
{
if(expr instanceof E_LogicalAnd) {
E_LogicalAnd e = (E_LogicalAnd)expr;
collectAnd(e.getArg1(), list);
collectAnd(e.getArg2(), list);
}
else if(expr instanceof E_LogicalOr) {
//List ors = new ArrayList();
ExprList ors = new ExprList();
collectOr(expr, ors);
list.add(ors);
} else {
list.add(new ExprList(expr));
}
}
public static void collectOr(Expr expr, ExprList list)
{
if(expr instanceof E_LogicalOr) {
E_LogicalOr e = (E_LogicalOr)expr;
collectOr(e.getArg1(), list);
collectOr(e.getArg2(), list);
} else {
list.add(expr);
}
}
public static Expr eval(Expr expr)
{
if(expr instanceof ExprFunction) {
return handle((ExprFunction)expr);
} else {
return expr;
}
}
public static Expr handle(ExprFunction expr)
{
//System.out.println("Converting to KNF: [" + expr.getClass() + "]: " + expr);
// not(and(A, B)) -> or(not A, not B)
// not(or(A, B)) -> or(not A, not B)
if(expr instanceof E_LogicalNot) {
Expr tmp = ((E_LogicalNot)expr).getArg();
if (!(tmp instanceof ExprFunction)) {
return expr;
}
ExprFunction child = (ExprFunction)tmp;
Expr newExpr = expr;
if (child instanceof E_LogicalAnd) {
newExpr = new E_LogicalOr(eval(new E_LogicalNot(child.getArg(1))), eval(new E_LogicalNot(child.getArg(2))));
}
else if (child instanceof E_LogicalOr) {
newExpr = new E_LogicalAnd(eval(new E_LogicalNot(child.getArg(1))), eval(new E_LogicalNot(child.getArg(2))));
}
else if (child instanceof E_LogicalNot) { // Remove double negation
newExpr = eval(child.getArg(1));
}
else {
return expr;
}
return eval(newExpr);
}
else if (expr instanceof E_LogicalAnd) {
//return expr;
//return eval(expr);
return new E_LogicalAnd(eval(expr.getArg(1)), eval(expr.getArg(2)));
}
/* Given:
* (A or B) AND (C x D) becomes:
* (A and (C x D)) OR (B and (c x D))
*
*
* (A or B) AND (C or D)
*
* Goal:
* (A and C) OR (A and D) OR (B and C) OR (B and D)
*
* This method transforms any "or" children of an AND node.
* other nodes are left untouched:
* (A or B) AND (c x D) becomes:
* (A and (c x D)) OR (B and (c x D))
*/
else if (expr instanceof E_LogicalOr) {
Expr aa = eval(expr.getArg(1));
Expr bb = eval(expr.getArg(2));
E_LogicalAnd a = null;
Expr b = null;
if (aa instanceof E_LogicalAnd) {
a = (E_LogicalAnd)aa;
b = bb;
}
else if(bb instanceof E_LogicalAnd) {
a = (E_LogicalAnd)bb;
b = aa;
}
if(a == null) {
return new E_LogicalOr(aa, bb);
} else {
return new E_LogicalAnd(eval(new E_LogicalOr(a.getArg(1), b)), eval(new E_LogicalOr(a.getArg(2), b)));
}
}
else if (expr instanceof E_NotEquals) { // Normalize (a != b) to !(a = b) --- this makes it easier to find "a and !a" cases
return new E_LogicalNot(eval(new E_Equals(expr.getArg(1), expr.getArg(2))));
}
return expr;
}
}
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