`/*
* (c) Copyright 2006, 2007, 2008 Hewlett-Packard Development Company, LP
* All rights reserved.
* [See end of file]
*/
package arq.examples.propertyfunction;
import java.util.List;
import com.hp.hpl.jena.graph.Node;
import com.hp.hpl.jena.graph.Triple;
import com.hp.hpl.jena.query.Query;
import com.hp.hpl.jena.query.QueryBuildException;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.query.QueryFactory;
import com.hp.hpl.jena.query.ResultSet;
import com.hp.hpl.jena.query.ResultSetFormatter;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;
import com.hp.hpl.jena.rdf.model.Resource;
import com.hp.hpl.jena.sparql.algebra.Algebra;
import com.hp.hpl.jena.sparql.algebra.Op;
import com.hp.hpl.jena.sparql.algebra.Table;
import com.hp.hpl.jena.sparql.algebra.TableFactory;
import com.hp.hpl.jena.sparql.algebra.op.OpBGP;
import com.hp.hpl.jena.sparql.algebra.op.OpFilter;
import com.hp.hpl.jena.sparql.algebra.op.OpJoin;
import com.hp.hpl.jena.sparql.algebra.op.OpTable;
import com.hp.hpl.jena.sparql.core.BasicPattern;
import com.hp.hpl.jena.sparql.core.Var;
import com.hp.hpl.jena.sparql.engine.ExecutionContext;
import com.hp.hpl.jena.sparql.engine.QueryIterator;
import com.hp.hpl.jena.sparql.engine.iterator.QueryIterNullIterator;
import com.hp.hpl.jena.sparql.engine.main.QC;
import com.hp.hpl.jena.sparql.expr.E_Regex;
import com.hp.hpl.jena.sparql.expr.Expr;
import com.hp.hpl.jena.sparql.expr.ExprVar;
import com.hp.hpl.jena.sparql.pfunction.PropFuncArg;
import com.hp.hpl.jena.sparql.pfunction.PropertyFunction;
import com.hp.hpl.jena.sparql.pfunction.PropertyFunctionRegistry;
import com.hp.hpl.jena.sparql.syntax.ElementFilter;
import com.hp.hpl.jena.sparql.syntax.ElementGroup;
import com.hp.hpl.jena.sparql.syntax.ElementTriplesBlock;
import com.hp.hpl.jena.sparql.util.ALog;
import com.hp.hpl.jena.sparql.util.NodeUtils;
import com.hp.hpl.jena.vocabulary.RDFS;
/** Example extension or property function to show rewriting part of a query.
* A simpler, more driect way to implement property functions is to extends
* one of the helper classes and have the custom code called on each solution from the
* the previosu query stage.
*
* See examples {@link localname} for a general predicate that allows for any of
* subject or object to be a variable of boudn value, or see {@link uppercase} for a simple
* implementation that transforms on graph node into a new node.
*
* This is a more complicated example which uses the PropertyFunction interface directly.
* It takes the QueryIterator from the previous stage and inserts a new processing step.
* It then calls that processing step to do the real work.
*
* The approach here could be used to access an external index (e.g. Lucene) although here
* we just show looking for RDFS labels.
*
* <pre>
* ?x ext:labelSearch "something"
* </pre>
* as
* <pre>
* ?x rdfs:label ?label . FILTER regex(?label, "something", "i")
* </pre>
*
* by simply doing a regex but could be used to add access to some other form of
* indexing or external structure.
*
* @author Andy Seaborne
*/
public class labelSearch implements PropertyFunction
{
List myArgs = null;
public void build(PropFuncArg argSubject, Node predicate, PropFuncArg argObject, ExecutionContext execCxt)
{
if ( argSubject.isList() || argObject.isList() )
throw new QueryBuildException("List arguments to "+predicate.getURI()) ;
}
/* This be called once, with unevaluated arguments.
* To do a rewrite of part of a query, we must use the fundamental PropertyFunction
* interface to be called once with the input iterator.
* Must not return null nor throw an exception. Instead, return a QueryIterNullIterator
* indicating no matches.
*/
public QueryIterator exec(QueryIterator input, PropFuncArg argSubject, Node predicate, PropFuncArg argObject, ExecutionContext execCxt)
{
// No real need to check the pattern arguments because
// the replacement triple pattern and regex will cope
// but we illustrate testing here.
Node nodeVar = argSubject.getArg() ;
String pattern = NodeUtils.stringLiteral(argObject.getArg()) ;
if ( pattern == null )
{
ALog.warn(this, "Pattern must be a plain literal or xsd:string: "+argObject.getArg()) ;
return new QueryIterNullIterator(execCxt) ;
}
if ( false )
// Old (ARQ 1) way - not recommended.
return buildSyntax(input, nodeVar, pattern, execCxt) ;
// Better
// Build a SPARQL algebra expression
Var var2 = createNewVar() ; // Hidden variable
BasicPattern bp = new BasicPattern() ;
Triple t = new Triple(nodeVar, RDFS.label.asNode(), var2) ;
bp.add(t) ;
OpBGP op = new OpBGP(bp) ;
Expr regex = new E_Regex(new ExprVar(var2.getName()), pattern, "i") ;
Op filter = OpFilter.filter(regex, op) ;
// ---- Evaluation
if ( true )
{
// Use the reference query engine
// Create a table for the input stream (so it uses working memory at this point,
// which is why this is not the preferred way).
// Then join to expression for this stage.
Table table = TableFactory.create(input) ;
Op op2 = OpJoin.create(OpTable.create(table), filter) ;
return Algebra.exec(op2, execCxt.getDataset()) ;
}
// Use the default, optimizing query engine.
return QC.execute(filter, input, execCxt) ;
}
// Build SPARQL syntax and compile it.
// Not recommended.
private QueryIterator buildSyntax(QueryIterator input, Node nodeVar, String pattern, ExecutionContext execCxt)
{
Var var2 = createNewVar() ;
// Triple patterns for ?x rdfs:label ?hiddenVar
ElementTriplesBlock elementBGP = new ElementTriplesBlock();
Triple t = new Triple(nodeVar, RDFS.label.asNode(), var2) ;
elementBGP.addTriple(t) ;
// Regular expression for regex(?hiddenVar, "pattern", "i")
Expr regex = new E_Regex(new ExprVar(var2.getName()), pattern, "i") ;
ElementGroup elementGroup = new ElementGroup() ;
elementGroup.addElement(elementBGP) ;
elementGroup.addElement(new ElementFilter(regex)) ;
// Compile it.
// The better design is to build the Op structure programmatically,
Op op = Algebra.compile(elementGroup) ;
op = Algebra.optimize(op, execCxt.getContext()) ;
return QC.execute(op, input, execCxt) ;
}
static int hiddenVariableCount = 0 ;
// Create a new, hidden, variable.
private static Var createNewVar()
{
hiddenVariableCount ++ ;
String varName = "-search-"+hiddenVariableCount ;
return Var.alloc(varName) ;
}
// -------- Example usage
public static void main(String[] argv)
{
// Call the function as java:arq.examples.ext.labelSearch or register it.
String prologue = "PREFIX ext: <java:arq.examples.propertyfunction.>\n" ;
String qs = prologue+"SELECT * { ?x ext:labelSearch 'EF' }" ;
Query query = QueryFactory.create(qs) ;
Model model = make() ;
QueryExecution qExec = QueryExecutionFactory.create(query, model) ;
try {
ResultSet rs = qExec.execSelect() ;
ResultSetFormatter.out(rs) ;
} finally { qExec.close() ; }
// Or register it.
PropertyFunctionRegistry.get().put("http://example/f#search", labelSearch.class) ;
prologue = "PREFIX ext: <http://example/f#>\n" ;
qs = prologue+"SELECT * { ?x ext:search 'EF' }" ;
query = QueryFactory.create(qs) ;
qExec = QueryExecutionFactory.create(query, model) ;
try {
ResultSet rs = qExec.execSelect() ;
ResultSetFormatter.out(rs) ;
} finally { qExec.close() ; }
}
private static Model make()
{
String BASE = "http://example/" ;
Model model = ModelFactory.createDefaultModel() ;
model.setNsPrefix("", BASE) ;
Resource r1 = model.createResource(BASE+"r1") ;
Resource r2 = model.createResource(BASE+"r2") ;
r1.addProperty(RDFS.label, "abc") ;
r2.addProperty(RDFS.label, "def") ;
return model ;
}
}
/*
* (c) Copyright 2006, 2007, 2008 Hewlett-Packard Development Company, LP
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/`