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Java > Open Source Codes > org > xquark > extractor > algebra > BinaryAlgebra


1 /*
2  * This file belongs to the XQuark distribution.
3  * Copyright (C) 2003 Universite de Versailles Saint-Quentin.
4  *
5  * This program is free software; you can redistribute it and/or
6  * modify it under the terms of the GNU Lesser General Public
7  * License as published by the Free Software Foundation; either
8  * version 2.1 of the License, or (at your option) any later version.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13  * Lesser General Public License for more details.
14  *
15  * You should have received a copy of the GNU Lesser General Public
16  * License along with this program; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307.
18  * You can also get it at http://www.gnu.org/licenses/lgpl.html
19  *
20  * For more information on this software, see http://www.xquark.org.
21  */
22
23 package org.xquark.extractor.algebra;
24
25 import java.util.Collections JavaDoc;
26 import java.util.List JavaDoc;
27 import java.util.Set JavaDoc;
28
29 public abstract class BinaryAlgebra extends BinaryOperator implements Relation
30 {
31     private static final String JavaDoc RCSRevision = "$Revision: 1.5 $";
32     private static final String JavaDoc RCSName = "$Name: $";
33
34     List JavaDoc _keys;
35     Set JavaDoc _providedTableInstance = Collections.singleton(this);
36
37     public BinaryAlgebra(Expression leftOperand, Expression rightOperand)
38     {
39         super (leftOperand,rightOperand);
40     }
41
42     public Set JavaDoc providedTableInstances() {
43         return _providedTableInstance;
44     };
45
46     public AttributeExpression findNonNullAttribute() {
47         AttributeExpression ret = ((Relation)_leftOperand).findNonNullAttribute();
48         if (ret == null)
49             ret = ((Relation)_rightOperand).findNonNullAttribute(); // QUESTION: is it necessary. Relation should not be identical ?
50 return ret;
51     }
52
53     public List JavaDoc getItems() { return null;}
54
55     public List JavaDoc getKeys()
56     {
57         return _keys;
58     }
59
60     public List JavaDoc nameTest(String JavaDoc name)
61     {
62         return ((Relation)getLeftOperand()).nameTest(name);
63     }
64
65
66     public boolean replaceChild(Expression oldChild, Expression newChild)
67     {
68         /* implementation for Merge, Union, Intersect and Difference, but not for OuterJoin */
69         boolean retVal = false;
70         if (getLeftOperand() == oldChild) {
71             setLeftOperand(newChild);
72             retVal = true;
73         }
74         else if (getRightOperand()== oldChild) {
75             setRightOperand(newChild);
76             retVal = true;
77         }
78
79         return retVal;
80     }
81 }
82
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