LessThanBuiltin.java

// OO jDREW - An Object Oriented extension of the Java Deductive Reasoning Engine for the Web
// Copyright (C) 2005 Marcel Ball
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

package org.ruleml.oojdrew.Builtins;

import java.util.Vector;

import org.ruleml.oojdrew.util.DefiniteClause;
import org.ruleml.oojdrew.util.SymbolTable;
import org.ruleml.oojdrew.util.Term;
import org.ruleml.oojdrew.util.Types;

/**
 * Implements a Less Than built-in relation.
 *
 * The call format is lessThan(?var, input).
 *
 * <p>Title: OO jDREW</p>
 *
 * <p>Description: Reasoning Engine for the Semantic Web - Supporting OO RuleML
 * 0.88</p>
 *
 * <p>Copyright: Copyright (c) 2005</p>
 *
 * @author Marcel A. Ball
 * @version 0.89
 */
public class LessThanBuiltin implements Builtin {
    private int sym = SymbolTable.internSymbol("lessThan");

    public DefiniteClause buildResult(Term t) {
        if (t.getSymbol() != sym) {
            return null;
        }

        if (t.subTerms.length != 3) {
            return null;
        }

        Term p1 = t.subTerms[1].deepCopy();
        Term p2 = t.subTerms[2].deepCopy();

        if (p1.getSymbol() < 0 || p2.getSymbol() < 0) {
            return null;
        }

        String p1s = p1.getSymbolString();
        String p2s = p2.getSymbolString();

        if ((p1.getType() == Types.IFLOAT || p1.getType() == Types.IINTEGER) &&
            (p2.getType() == Types.IFLOAT || p2.getType() == Types.IINTEGER)) {
            double d1;
            double d2;
            try {
                d1 = Double.parseDouble(p1s);
                d2 = Double.parseDouble(p2s);
            } catch (Exception e) {
                return null;
            }
            if (d1 >= d2) {
                return null;
            }
        } else if (p1.getType() == Types.ISTRING &&
                   p2.getType() == Types.ISTRING) {
            if (p1s.compareTo(p2s) >= 0) {
                return null;
            }
        } else {
            return null;
        }

        Term roid = new Term(SymbolTable.internSymbol("$jdrew-lt-"
                                                      + p1s + "<" + p2s),
                             SymbolTable.IOID, Types.ITHING);

        Vector v = new Vector();
        v.add(roid);
        v.add(p1);
        v.add(p2);

        Term atm = new Term(sym, SymbolTable.INOROLE, Types.IOBJECT, v);
        atm.setAtom(true);
        Vector v2 = new Vector();
        v2.add(atm);
        return new DefiniteClause(v2, new Vector());
    }

    public int getSymbol() {
        return this.sym;
    }
}