/*
* The contents of this file are subject to the Mozilla Public License
* Version 1.1 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is the Kowari Metadata Store.
*
* The Initial Developer of the Original Code is Plugged In Software Pty
* Ltd (http://www.pisoftware.com, mailto:info@pisoftware.com). Portions
* created by Plugged In Software Pty Ltd are Copyright (C) 2001,2002
* Plugged In Software Pty Ltd. All Rights Reserved.
*
* Contributor(s): N/A.
*
* [NOTE: The text of this Exhibit A may differ slightly from the text
* of the notices in the Source Code files of the Original Code. You
* should use the text of this Exhibit A rather than the text found in the
* Original Code Source Code for Your Modifications.]
*
*/
package org.mulgara.query;
/**
* Disjunction of conjunctions with serial access to each of the disjoined
* terms.
*
* A cursor is a set of solutions, where a solution is a mapping of
* {@link Variable}s to some type specified by the subinterface.
* This is similar to a JDBC {@link java.sql.ResultSet}.
*
* @created 2004-03-12
*
* @author <a href="http://staff.pisoftware.com/raboczi">Simon Raboczi</a>
*
* @version $Revision: 1.9 $
*
* @modified $Date: 2005/01/28 00:28:37 $
*
* @maintenanceAuthor $Author: newmana $
*
* @company <A href="mailto:info@PIsoftware.com">Plugged In Software</A>
*
* @copyright ©2004 <a href="http://www.pisoftware.com/">Plugged In
* Software Pty Ltd</a>
*
* @licence <a href="{@docRoot}/../../LICENCE">Mozilla Public License v1.1</a>
*/
public interface Cursor {
public static final int ZERO = 0;
public static final int ONE = 1;
public static final int MANY = 2;
/**
* Reset to iterate through every single element.
*
* @throws TuplesException Due to an error accessing the underlying data.
*/
public void beforeFirst() throws TuplesException;
/**
* Free resources associated with this instance.
*
* @throws TuplesException Due to an error accessing the underlying data.
*/
public void close() throws TuplesException;
/**
* Find the index of a variable.
*
* @param column The variable to search for.
* @return The ColumnIndex value
* @throws TuplesException If the variable is null or not in this tuples.
*/
public int getColumnIndex(Variable column) throws TuplesException;
/**
* Returns the number of variables (columns).
*
* @return the number of variables (columns)
*/
public int getNumberOfVariables();
/**
* The variables bound and their default collation order. The array returned
* by this method should be treated as if its contents were immutable, even
* though Java won't enforce this. If the elements of the array are modified,
* there may be side effects on the past and future clones of the tuples it
* was obtained from.
*
* @return the {@link Variable}s bound within this answer.
*/
public Variable[] getVariables();
/**
* Tests whether this is a unit-valued answer. A unit answer appended to
* something yields the unit answer. A unit answer joined to something yields
* the same something. Notionally, the unit answer has zero columns and one
* row.
*
* @return The Unconstrained value
* @throws TuplesException Due to an error accessing the underlying data.
*/
public boolean isUnconstrained() throws TuplesException;
/**
* This method returns the exact number of rows which this instance contains.
*
* @return The exact number of rows that this instance contains.
* @throws TuplesException Due to an error accessing the underlying data.
*/
public long getRowCount() throws TuplesException;
/**
* This method returns an upper bound on the number of rows which this instance contains.
*
* @return The upper bound of the number of rows that this instance contains.
* @throws TuplesException Due to an error accessing the underlying data.
*/
public long getRowUpperBound() throws TuplesException;
/**
* This method returns the expected number of rows which this instance contains.
* This number should be updated statistically over time, when possible.
*
* @return An expected value for the rows.
* @throws TuplesException Due to an error accessing the underlying data.
*/
public long getRowExpectedCount() throws TuplesException;
/**
* This method returns cardinality of the number of rows which this instance contains.
*
* @return The cardinality of this tuples. {0,1,N} rows.
* @throws TuplesException Due to an error accessing the underlying data.
*/
public int getRowCardinality() throws TuplesException;
/**
* This method tests whether the cursor is known to be empty (i.e. have zero rows).
* It is intended for optimization purposes, when an empty test can be performed
* without actually evaluating the cursor. It is possible for this method to
* return <tt>false</tt> and still have zero rows, but if this method returns
* <tt>true</tt> then it is guaranteed that the cursor has zero rows.
*
* @return <tt>true</tt> if this cursor is known to contain no rows.
* @throws TuplesException Due to an error accessing the underlying data.
*/
public boolean isEmpty() throws TuplesException;
/**
* Move to the next row.
*
* If no such row exists, return <code>false<code> and the current row
* becomes unspecified. The current row is unspecified when an
* instance is created. To specify the current row, the
* {@link #beforeFirst()} method must be invoked
*
* @return whether a subsequent row exists
* @throws IllegalStateException if the current row is unspecified.
* @throws TuplesException Due to an error accessing the underlying data.
*/
public boolean next() throws TuplesException;
}