/*******************************************************************************
* Copyright (C) 2008-2012 Dominik Jain.
*
* This file is part of ProbCog.
*
* ProbCog is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* ProbCog is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with ProbCog. If not, see <http://www.gnu.org/licenses/>.
******************************************************************************/
package probcog.logic;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.Vector;
import probcog.logic.parser.FormulaParser;
import probcog.logic.parser.ParseException;
import probcog.srl.Database;
import probcog.srl.GenericDatabase;
import probcog.srl.RelationalModel;
/**
* Abstract base class for logical formulas.
* @author Dominik Jain
*/
public abstract class Formula {
/**
* gets a mapping from names of meta-variables appearing in the formula to the types/domains they apply to
* @param db
* @param ret mapping in which to store the result
* @throws Exception
*/
public abstract void getVariables(GenericDatabase<?, ?> db, Map<String,String> ret) throws Exception;
/**
* adds any constants appearing in the formula to the given relational model
* @param m
*/
public abstract void addConstantsToModel(RelationalModel m) throws Exception;
/**
* grounds this formula for a particular binding of its variables
* @param binding the variable binding
* @param worldVars the set of ground atoms (which is needed to return the ground versions of atoms)
* @param db a database containing a set of constants for each type that can be used to ground quantified formulas (can be null if the formula does not contain any quantified variables)
* @return
* @throws Exception
*/
public abstract Formula ground(Map<String, String> binding, WorldVariables worldVars, GenericDatabase<?, ?> db) throws Exception;
/**
* gets the set of ground atoms appearing in this (grounded) formula
* @param ret the set to write to
*/
public abstract void getGroundAtoms(Set<GroundAtom> ret);
public abstract boolean isTrue(IPossibleWorld w);
public enum FormulaSimplification {
/**
* perform no simplification
*/
None,
/**
* perform simplification, removing trivial groundings that reduce to True or False
*/
On,
/**
* do simplification, throwing an exception if a ground formula is simplified to False
*/
OnDisallowFalse
}
/**
* gets a list of all groundings of the formula for a particular set of objects
* @param db the database containing all relevant constant symbols (objects) to use for grounding
* @param worldVars the collection of variables (ground atoms) that defines the set of possible worlds
* @param simplify whether to use the evidence in the database to simplify ground formulas
* @return
* @throws Exception
*/
public Vector<Formula> getAllGroundings(Database db, WorldVariables worldVars, FormulaSimplification simplify) throws Exception {
Vector<Formula> ret = new Vector<Formula>();
addAllGroundingsTo(ret, db, worldVars, simplify);
return ret;
}
/**
* generates all groundings and adds them to the given collection
* @param collection
* @param db
* @param worldVars
* @param simplify whether to use the evidence in the database to simplify ground formulas
* @throws Exception
*/
public void addAllGroundingsTo(Collection<Formula> collection, Database db, WorldVariables worldVars, FormulaSimplification simplify) throws Exception {
HashMap<String, String> vars = new HashMap<String, String>();
getVariables(db, vars);
String[] varNames = vars.keySet().toArray(new String[vars.size()]);
generateGroundings(collection, db, new HashMap<String, String>(), varNames, 0, vars, worldVars, simplify);
}
/**
* recursively generates groundings of the formula
* @param ret the collection in which to store the generated groundings
* @param db the database in which all usable constant symbols are found
* @param binding a mapping of variable names to constant names
* @param varNames the variables that are to be grounded
* @param i the current index of the variable in varNames to ground next
* @param var2domName a mapping of variable names to domain names (that contains as keys at least the variables in varNames)
* @param worldVars the collection of variables (ground atoms) that defines the set of possible worlds
* @param simplify whether to use the evidence in the database to simplify ground formulas
* @throws Exception
*/
protected void generateGroundings(Collection<Formula> ret, GenericDatabase<?,?> db, Map<String, String> binding, String[] varNames, int i, Map<String, String> var2domName, WorldVariables worldVars, FormulaSimplification simplify) throws Exception {
// if we have the full set of parameters, add it to the collection
if(i == varNames.length) {
Formula f = (this.ground(binding, worldVars, db));
if(simplify != FormulaSimplification.None)
f = f.simplify(db);
if(f instanceof TrueFalse) {
if(!((TrueFalse)f).isTrue() && simplify == FormulaSimplification.OnDisallowFalse)
throw new Exception("Unsatisfiable hard formula encountered: " + this.toString() + " with binding " + binding.toString() + " cannot be satisfied (given the evidence).");
return;
}
else
ret.add(f);
return;
}
// otherwise consider all ways of extending the current list of parameters using the domain elements that are applicable
String varName = varNames[i];
String domName = var2domName.get(varName);
Iterable<String> domain = db.getDomain(domName);
if(domain == null)
throw new Exception("Domain named '" + domName + "' (of variable " + varName + " in formula " + this.toString() + ") not found in the database!");
for(String element : domain) {
binding.put(varName, element);
generateGroundings(ret, db, binding, varNames, i+1, var2domName, worldVars, simplify);
}
}
/**
* convert the formula to conjunctive normal form
* @return a CNF formula
*/
public abstract Formula toCNF();
/**
* convert the formula to negation normal form
* @return an NNF formula
*/
public abstract Formula toNNF();
/**
* simplifies the formula by removing parts of the formula that can be evaluated
* @param evidence an evidence database with which to evaluate ground atoms (may be null; if null, will only simplify based on TrueFalse instances appearing within the formula)
* @return a simplified version of the formula that incorporates the evidence
*/
public abstract Formula simplify(GenericDatabase<?, ?> evidence);
public static Formula fromString(String f) throws ParseException {
return FormulaParser.parse(f);
}
public static void main(String[] args) throws ParseException {
String s = "a(x) <=> b(x)";
//s = "a(x) v (b(x) ^ c(x))";
//s = "(a(x) v (b(x) ^ c(x))) => f(x)";
s = "(a(x) ^ b(x) ^ !c(x) ^ !d(x)) v (a(x) ^ !b(x) ^ c(x) ^ !d(x)) v (!a(x) ^ b(x) ^ c(x) ^ !d(x)) v (a(x) ^ !b(x) ^ !c(x) ^ d(x)) v (!a(x) ^ b(x) ^ !c(x) ^ d(x)) v (!a(x) ^ !b(x) ^ c(x) ^ d(x))";
Formula f = fromString(s);
System.out.println("CNF: " + f.toCNF().toString());
}
}