/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
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 General Public License for more details.
You should have received a copy of the GNU 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 USA
*/
/*
* Created on Sep 20, 2010
*/
package com.bigdata.bop.bset;
import java.util.Map;
import com.bigdata.bop.BOp;
import com.bigdata.bop.BOpEvaluationContext;
import com.bigdata.bop.PipelineOp;
import com.bigdata.bop.controller.Union;
import com.bigdata.bop.join.PipelineJoin;
import com.bigdata.rdf.rules.TMUtility;
import com.bigdata.relation.RelationFusedView;
import com.bigdata.relation.rule.Slice;
/**
* TEE(op):[sinkRef=X; altSinkRef=Y]
* <p>
* Pipeline operator copies its source to both sink and altSink. The sink and
* the altSink must both be ancestors of the operator. The sinkRef MAY be
* omitted when one of the targets is the immediate parent of the TEE.
* Evaluation scope: {@link BOpEvaluationContext#ANY}.
* <p>
* <h2>Example - Truth Maintenance</h2>
* <p>
* In truth maintenance we establish a focus store which is brought to a fixed
* point by applying some rules and a transitive closure operator. Once the
* fixed point is reached, the assertions in the focus store are either inserted
* onto the database or (for retraction) removed from database unless a proof
* can be found that an assertion is still entailed.
* <p>
* The {@link Tee} operator can be used in truth maintenance to read on the
* UNION of the focus store and the database - see {@link TMUtility}. This is
* handled as the "union" of two JOINs using a {@link Tee} as follows:
*
* <pre>
* slice := SLICE( join2 )[bopId=3]
* join2 := JOIN( join1, bar.spo(A,loves,B))[bopId=2]
* join1 := JOIN( tee, foo.spo(A,loves,B))[bopId=1; sinkRef=3]
* tee := TEE( ... )[altSinkRef=2],
* </pre>
*
* The {@link Tee} copies its inputs to both the default sink (its parent, which
* is join1) and the alternate sink (join2). join1 routes its outputs around
* join2, sending them directly to their lowest common ancestor. This has the
* effect of creating a union of their outputs at the receiver. In this example,
* a {@link Slice} is used as the target for both of the join operators. Since
* this is a pipeline construction, the joins will be evaluated in parallel as
* intermediate results arrive for those operators. Normally the {@link Tee}
* will be fed by a {@link StartOp} or another {@link PipelineJoin}.
*
* @todo The union of access paths was historically handled by
* {@link RelationFusedView}. That class should be removed once queries
* are rewritten to use the union of joins.
*
* @todo The {@link TMUtility} will have to be updated to use this operator
* rather than specifying multiple source "names" for the relation of the
* predicate.
*
* @todo The FastClosureRuleTask will also need to be updated to use a
* {@link Union} over the joins rather than a {@link RelationFusedView}.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class Tee extends CopyOp {
/**
*
*/
private static final long serialVersionUID = 1L;
/**
* Deep copy constructor.
* @param op
*/
public Tee(final Tee op) {
super(op);
}
/**
* Shallow copy constructor.
* @param args
* @param annotations
*/
public Tee(BOp[] args, Map<String, Object> annotations) {
super(args, annotations);
getRequiredProperty(PipelineOp.Annotations.ALT_SINK_REF);
}
}