/**
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 Dec 8, 2011
*/
package com.bigdata.bop.join;
import com.bigdata.bop.IPredicate;
/**
* A type safe enumeration of the different flavors of hash index "joins".
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public enum JoinTypeEnum {
/**
* A normal join. The output is the combination of the left and right hand
* solutions. Only solutions which join are output.
*/
Normal,
/**
* An optional join. The output is the combination of the left and right
* hand solutions. Solutions which join are output, plus any left solutions
* which did not join. Constraints on the join ARE NOT applied to the
* "optional" path.
*/
Optional,
/**
* A join where the left solution is output iff there exists at least one
* right solution which joins with that left solution. For each left
* solution, that solution is output either zero or one times. In order to
* enforce this cardinality constraint, the hash join logic winds up
* populating the "join set" and then outputs the join set once all
* solutions which join have been identified.
*/
Exists,
/**
* A join where the left solution is output iff there is no right solution
* which joins with that left solution. This basically an optional join
* where the solutions which join are not output.
* <p>
* Note: This is also used for "MINUS" since the only difference between
* "NotExists" and "MINUS" deals with the scope of the variables.
*/
NotExists,
/**
* A distinct filter (not a join). Only the distinct left solutions are
* output. Various annotations pertaining to JOIN processing are ignored
* when the hash index is used as a DISTINCT filter.
*/
Filter;
/**
* Return <code>true</code> iff this is a DISTINCT SOLUTIONS filter.
*
* @see #Filter
*/
public boolean isFilter() {
return this == Filter;
}
/**
* Return <code>true</code> iff this is a JOIN with OPTIONAL semantics.
*
* @see #Optional
* @see IPredicate.Annotations#OPTIONAL
*/
public boolean isOptional() {
return this == Optional;
}
/**
* Return <code>true</code> iff this is a {@link #Normal} join.
*/
public boolean isNormal() {
return this == Normal;
}
}