/**
 *        CloudGraph Community Edition (CE) License
 * 
 * This is a community release of CloudGraph, a dual-license suite of
 * Service Data Object (SDO) 2.1 services designed for relational and 
 * big-table style "cloud" databases, such as HBase and others. 
 * This particular copy of the software is released under the 
 * version 2 of the GNU General Public License. CloudGraph was developed by 
 * TerraMeta Software, Inc.
 * 
 * Copyright (c) 2013, TerraMeta Software, Inc. All rights reserved.
 * 
 * General License information can be found below.
 * 
 * This distribution may include materials developed by third
 * parties. For license and attribution notices for these
 * materials, please refer to the documentation that accompanies
 * this distribution (see the "Licenses for Third-Party Components"
 * appendix) or view the online documentation at 
 * <http://cloudgraph.org/licenses/>. 
 */
package org.cloudgraph.mapreduce;

import java.io.IOException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.mapreduce.Mapper;

/**
 * Supplies fully realized data {@link GraphWritable graphs} as the input value to MapReduce <code>Mapper</code> 
 * client subclasses, the input key being an offset into the processed file and the 
 * value being a {@link GraphWritable} assembled from a single SDO graph XML line read from the file. 
 * Supports detection of changes to the input data graph, and propagation of mutations
 * to the underlying data store. 
 *    
 * The data graphs supplied to the code>Mapper</code> are ready to further modify or simply commit as is, 
 * for <code>Mapper</code> clients wishing to modify input graphs and 
 * commit changes within the map phase. See the below code sample based on the Wikipedia domain model
 * which adds a page link to each input graph.  
 *<p>
 *<pre>
 *public class PageGraphImporter extends GraphXmlMapper<LongWritable, GraphWritable> {
 *    @Override
 *    public void map(LongWritable offset, GraphWritable graph, Context context) throws IOException {
 *    
 *        Page page = (Page)graph.getDataGraph().getRootObject();
 *        page.setPageTitle("New Page1");
 *
 *        // commit above changes
 *        super.commit(row, graph, context);
 *    }
 *}
 *</pre>
 *</p>
 * 
 * <p>
 * Data graphs of any size of complexity may be supplied to MapReduce jobs including graphs where the underlying
 * domain model contains instances of multiple inheritance. The set of data graphs is provided to
 * a MapReduce job using a <a href="http://plasma-sdo.org/org/plasma/query/Query.html">query</a>, typically 
 * supplied using {@link GraphMapReduceSetup}.    
 * </p>
 * <p>
 * Data graphs are assembled within a {@link GraphXmlRecordReader} based on the line oriented XML graph data read
 * from an underlying file, and are passed to client {@link GraphXmlMapper} extensions.   
 * </p>
 * 
 * @param <KEYOUT> the output key type
 * @param <VALUEOUT> the output value type
 * 
 * @see org.cloudgraph.mapreduce.GraphWritable
 * @see org.cloudgraph.mapreduce.GraphXmlRecordReader
 * @see org.cloudgraph.hbase.mapreduce.GraphMapReduceSetup
 * 
 * @author Scott Cinnamond
 * @since 0.5.8
 */
public class GraphXmlMapper<KEYOUT, VALUEOUT>
    extends Mapper<LongWritable, GraphWritable, KEYOUT, VALUEOUT> {
	
    private static Log log = LogFactory.getLog(GraphXmlMapper.class);
	
	public GraphXmlMapper() {
	}
	
	@Override
	public void map(LongWritable row, GraphWritable graph,
			Context context) throws IOException {
        //no behavior
	}
	
}