Relation


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.List  ;
26  import java.util.Set  ;
27  
28  public interface Relation
29  {
30      /**
31       * Browse recursively operands for {@link Table} stopping on projections and
32       * BinaryAlgebra operations which are returned in place.
33       * Returns a set of {@link Relation} containing the same elements that
34       * {@link #visibleTableInstances()} for joins and {@link UnaryAlgebra} (group,
35       * sort, restrictions), and "this" for {@link BinaryAlgebra} (unions and
36       * other set operations), tables and projections.
37       * @return a cached object to clone if modification needed. 
38       */
39      public Set   providedTableInstances();
40  
41      /**
42       * Browse recursively operands returning union of {@link Relation#providedTableInstances()}.
43       * Returns a set of {@link Relation} containing the union of 
44       * {@link #providedTableInstances()} results on every operand and "this" for
45       * table nodes.
46       * To summerize, recursive search is performed almost as for {@link #providedTableInstances()}
47       * but one level (the operand level) is at least browsed so calling this
48       * method on a projection or a union will return the table(s) being
49       * projected contrary to {@link #providedTableInstances()}.
50       * @return a cached object to clone if modification needed. 
51       */
52      public Set   visibleTableInstances();
53  
54      /**
55       */
56      public List   getKeys();
57  
58      /**
59       * Returns a list of items available in current subtree with a specified name.
60       * Uses responsibility chain.
61       * @param name the item name to be searched for.
62       * @return List a list of {@link Expression}
63       */
64      public List   nameTest(String   name);
65  
66      /**
67       * Browse relation attributes until finding a non-nullable one.
68       * @return null if all relation attributes are nullable or relation has no attributes.
69       */
70      public AttributeExpression findNonNullAttribute();
71  }
72
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