trunk/workflowmodel-api/src/main/java/net/sf/taverna/t2/workflowmodel/Merge.java

/*******************************************************************************
 * Copyright (C) 2007 The University of Manchester   
 * 
 *  Modifications to the initial code base are copyright of their
 *  respective authors, or their employers as appropriate.
 * 
 *  This program 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 program 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 program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 ******************************************************************************/
package net.sf.taverna.t2.workflowmodel;

import java.util.List;

/**
 * Allows multiple outputs to be routed to a single input within the dataflow.
 * The merge operation defines a total order over its input ports, this order is
 * used to modify the index array of all incoming events by adding the port
 * index as a prefix to that array. At a conceptual level this means that any
 * event coming in is 'binned' by port index creating a collection of whatever
 * the port type was. This also places a constraint that all input ports must
 * have the same cardinality (i.e. depth + length of index array must be equal
 * for all events on all ports). If this constraint is violated the merge
 * operation is free to throw a WorkflowStructureException at runtime although
 * it would be preferable if implementing classes were capable of static type
 * analysis to preclude this from happening.
 * 
 * @author Tom Oinn
 * 
 */
public interface Merge extends TokenProcessingEntity {

	/**
	 * The Merge object contains an ordered list of InputPort objects. Data and
	 * completion events arriving at an input port have the index of that input
	 * within the list prepended to their index array, effectively placing them
	 * in a virtual collection the top level of which corresponds to the various
	 * input ports defined within the Merge node. When final completion events
	 * from all input ports are received the Merge object registers the top
	 * level collection with the attached DataManager and emits it and the
	 * completion event through the single output port.
	 * 
	 * @return Ordered list of InputPort objects
	 */
	List<? extends MergeInputPort> getInputPorts();

	/**
	 * The Merge object has a single output port through which modified events
	 * are emitted as described in the javadoc for getInputPorts
	 * 
	 * @return OutputPort for this Merge object
	 */
	EventForwardingOutputPort getOutputPort();

}