/*
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 Jun 23, 2008
*/
package com.bigdata.relation.rule;
import java.util.Iterator;
import com.bigdata.bop.IPredicate;
import com.bigdata.relation.IMutableRelation;
import com.bigdata.relation.rule.eval.ISolution;
/**
* A program consists of a set of rules and/or programs. Some programs are
* executed sequentially while others are (at least logically) parallel. A
* program may also specify the transitive closure of its rules.
*
* @todo add an XML (de-)serialization for programs and rules so that the rule
* sets may be declared. Note that there are a few very specialized rules
* whose semantics might not be fully declarable for the fast closure
* method used by the RDF KB.
*
* @todo Make it possible for people to easily extend the RDF KB rule sets or
* run rules over a RDF data set, but note that there are interactions in
* the rules choosen for evaluation during forward closure and those
* choosen for evaluation at query time.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public interface IProgram extends IStep {
/**
* <code>true</code> iff the {@link #steps()} MAY be executed in parallel.
* When <code>false</code> the steps WILL be executed sequentially and
* (for mutation) the buffered writes will be flushed after each step.
* <p>
* Note: Sequential execution of a program makes a multi-{@link IRule}
* program MUCH easier to debug as the rules are executed one by one and the
* buffer is flushed after each rule so you can directly see the #of
* elements consider by the {@link IRule} for each {@link IPredicate} in the
* tail and the #of {@link ISolution}s generated by the {@link IRule}.
*/
boolean isParallel();
/**
* <code>true</code> iff the fixed point closure of the {@link IProgram}
* should be computed.
* <p>
* Note: Closure is computed in rounds. The rounds continue until the
* {@link IMutableRelation}(s) on which the steps are writing reach a fixed
* point (no new solutions are added to the relation(s) within a given
* round). If a program has a fixed point, then the same closure will be
* obtained by either sequential or parallel execution of the steps within
* each round and in general parallel execution of the steps is perferred as
* it has better performance. However, the steps MAY be executed
* sequentially to facilitate debugging.
*/
boolean isClosure();
/**
* The sequence of sub-program {@link IStep}s.
*/
Iterator<IStep> steps();
/**
* The #of steps in the program (non-recursive).
*/
public int stepCount();
/**
* An array containing the steps in the program (non-recursive).
*/
public IStep[] toArray();
}