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Merge pull request LinkedDataFragments#58 from awoods/issue-57
Implement SPARQL datasource
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201 changes: 201 additions & 0 deletions
201
...in/java/org/linkeddatafragments/datasource/sparql/SparqlBasedRequestProcessorForTPFs.java
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| @@ -0,0 +1,201 @@ | ||
| package org.linkeddatafragments.datasource.sparql; | ||
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| import java.net.URI; | ||
| import java.net.URISyntaxException; | ||
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| import org.apache.http.client.utils.URIBuilder; | ||
| import org.apache.jena.query.ParameterizedSparqlString; | ||
| import org.apache.jena.query.Query; | ||
| import org.apache.jena.query.QueryExecution; | ||
| import org.apache.jena.query.QueryExecutionFactory; | ||
| import org.apache.jena.query.QueryFactory; | ||
| import org.apache.jena.query.QuerySolution; | ||
| import org.apache.jena.query.QuerySolutionMap; | ||
| import org.apache.jena.query.ResultSet; | ||
| import org.apache.jena.query.Syntax; | ||
| import org.apache.jena.rdf.model.Literal; | ||
| import org.apache.jena.rdf.model.Model; | ||
| import org.apache.jena.rdf.model.ModelFactory; | ||
| import org.apache.jena.rdf.model.RDFNode; | ||
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| import org.linkeddatafragments.datasource.AbstractRequestProcessorForTriplePatterns; | ||
| import org.linkeddatafragments.datasource.IFragmentRequestProcessor; | ||
| import org.linkeddatafragments.fragments.ILinkedDataFragment; | ||
| import org.linkeddatafragments.fragments.tpf.ITriplePatternElement; | ||
| import org.linkeddatafragments.fragments.tpf.ITriplePatternFragmentRequest; | ||
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| /** | ||
| * Implementation of {@link IFragmentRequestProcessor} that processes | ||
| * {@link ITriplePatternFragmentRequest}s over data stored behind a SPARQL-Query endpoint. | ||
| * | ||
| * @author <a href="mailto:[email protected]">Bart Hanssens</a> | ||
| * @author <a href="http://olafhartig.de">Olaf Hartig</a> | ||
| */ | ||
| public class SparqlBasedRequestProcessorForTPFs | ||
| extends AbstractRequestProcessorForTriplePatterns<RDFNode,String,String> | ||
| { | ||
| private final URI endpointURI; | ||
| private final String username; | ||
| private final String password; | ||
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| private final String sparql = "CONSTRUCT WHERE { ?s ?p ?o } "; | ||
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| private final String count = "SELECT (COUNT(?s) AS ?count) WHERE { ?s ?p ?o }"; | ||
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| private final Query query = QueryFactory.create(sparql, Syntax.syntaxSPARQL_11); | ||
| private final Query countQuery = QueryFactory.create(count, Syntax.syntaxSPARQL_11); | ||
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| /** | ||
| * | ||
| * @param request | ||
| * @return | ||
| * @throws IllegalArgumentException | ||
| */ | ||
| @Override | ||
| protected Worker getTPFSpecificWorker( | ||
| final ITriplePatternFragmentRequest<RDFNode,String,String> request ) | ||
| throws IllegalArgumentException | ||
| { | ||
| return new Worker( request ); | ||
| } | ||
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| /** | ||
| * | ||
| */ | ||
| protected class Worker | ||
| extends AbstractRequestProcessorForTriplePatterns.Worker<RDFNode,String,String> | ||
| { | ||
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| /** | ||
| * | ||
| * @param req | ||
| */ | ||
| public Worker( | ||
| final ITriplePatternFragmentRequest<RDFNode,String,String> req ) | ||
| { | ||
| super( req ); | ||
| } | ||
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| /** | ||
| * | ||
| * @param subject | ||
| * @param predicate | ||
| * @param object | ||
| * @param offset | ||
| * @param limit | ||
| * @return | ||
| */ | ||
| @Override | ||
| protected ILinkedDataFragment createFragment( | ||
| final ITriplePatternElement<RDFNode,String,String> subject, | ||
| final ITriplePatternElement<RDFNode,String,String> predicate, | ||
| final ITriplePatternElement<RDFNode,String,String> object, | ||
| final long offset, | ||
| final long limit ) | ||
| { | ||
| // FIXME: The following algorithm is incorrect for cases in which | ||
| // the requested triple pattern contains a specific variable | ||
| // multiple times; | ||
| // e.g., (?x foaf:knows ?x ) or (_:bn foaf:knows _:bn) | ||
| // see https://github.com/LinkedDataFragments/Server.Java/issues/24 | ||
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| QuerySolutionMap map = new QuerySolutionMap(); | ||
| if ( ! subject.isVariable() ) { | ||
| map.add("s", subject.asConstantTerm()); | ||
| } | ||
| if ( ! predicate.isVariable() ) { | ||
| map.add("p", predicate.asConstantTerm()); | ||
| } | ||
| if ( ! object.isVariable() ) { | ||
| map.add("o", object.asConstantTerm()); | ||
| } | ||
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| query.setOffset(offset); | ||
| query.setLimit(limit); | ||
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| Model triples = ModelFactory.createDefaultModel(); | ||
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| // Build the SPARQL-endpoint | ||
| URIBuilder uriBuilder = new URIBuilder(endpointURI); | ||
| addCredentials(uriBuilder); | ||
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| final String endpoint; | ||
| try { | ||
| endpoint = uriBuilder.build().toString(); | ||
| } catch (URISyntaxException e) { | ||
| throw new RuntimeException(e); | ||
| } | ||
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| ParameterizedSparqlString queryWithParams = new ParameterizedSparqlString(query.serialize(), map); | ||
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| try (QueryExecution qexec = QueryExecutionFactory.sparqlService(endpoint, queryWithParams.asQuery())) { | ||
| qexec.execConstruct(triples); | ||
| } | ||
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| if (triples.isEmpty()) { | ||
| return createEmptyTriplePatternFragment(); | ||
| } | ||
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| // Try to get an estimate | ||
| long size = triples.size(); | ||
| long estimate = -1; | ||
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| ParameterizedSparqlString countQueryWithParams = new ParameterizedSparqlString(countQuery.serialize(), map); | ||
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| try (QueryExecution qexec = QueryExecutionFactory.createServiceRequest(endpoint, countQueryWithParams.asQuery())) { | ||
| ResultSet results = qexec.execSelect(); | ||
| if (results.hasNext()) { | ||
| QuerySolution soln = results.nextSolution() ; | ||
| Literal literal = soln.getLiteral("count"); | ||
| estimate = literal.getLong(); | ||
| } | ||
| } | ||
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| /*GraphStatisticsHandler stats = model.getGraph().getStatisticsHandler(); | ||
| if (stats != null) { | ||
| Node s = (subject != null) ? subject.asNode() : null; | ||
| Node p = (predicate != null) ? predicate.asNode() : null; | ||
| Node o = (object != null) ? object.asNode() : null; | ||
| estimate = stats.getStatistic(s, p, o); | ||
| }*/ | ||
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| // No estimate or incorrect | ||
| if (estimate < offset + size) { | ||
| estimate = (size == limit) ? offset + size + 1 : offset + size; | ||
| } | ||
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| // create the fragment | ||
| final boolean isLastPage = ( estimate < offset + limit ); | ||
| return createTriplePatternFragment( triples, estimate, isLastPage ); | ||
| } | ||
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| /** | ||
| * This method adds 'email' and 'password' parameters to the provided URIBuilder | ||
| * Note: This credentials approach is very specific to the VIVO (https://github.com/vivo-project/VIVO) | ||
| * application and should be refactored once another use-case/example is required. | ||
| * | ||
| * @param uriBuilder of SPARQL-Query endpoint | ||
| */ | ||
| private void addCredentials(URIBuilder uriBuilder) { | ||
| if (username != null && password != null) { | ||
| uriBuilder.addParameter("email", username); | ||
| uriBuilder.addParameter("password", password); | ||
| } | ||
| } | ||
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| } // end of class Worker | ||
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| /** | ||
| * Constructor | ||
| * | ||
| * @param endpointURI of SPARQL-Query service | ||
| * @param username for SPARQL-Query service | ||
| * @param password for SPARQL-Query service | ||
| */ | ||
| public SparqlBasedRequestProcessorForTPFs(URI endpointURI, String username, String password) { | ||
| this.endpointURI = endpointURI; | ||
| this.username = username; | ||
| this.password = password; | ||
| } | ||
| } |
52 changes: 52 additions & 0 deletions
52
src/main/java/org/linkeddatafragments/datasource/sparql/SparqlDataSource.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,52 @@ | ||
| package org.linkeddatafragments.datasource.sparql; | ||
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| import java.io.File; | ||
| import java.net.URI; | ||
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| import org.linkeddatafragments.datasource.DataSourceBase; | ||
| import org.linkeddatafragments.datasource.IFragmentRequestProcessor; | ||
| import org.linkeddatafragments.fragments.IFragmentRequestParser; | ||
| import org.linkeddatafragments.fragments.tpf.TPFRequestParserForJenaBackends; | ||
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| /** | ||
| * Experimental SPARQL-endpoint-backed data source of Basic Linked Data Fragments. | ||
| * | ||
| * @author <a href="mailto:[email protected]">Bart Hanssens</a> | ||
| * @author <a href="http://olafhartig.de">Olaf Hartig</a> | ||
| * @author <a href="https://awoods.io">Andrew Woods</a> | ||
| */ | ||
| public class SparqlDataSource extends DataSourceBase { | ||
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| /** | ||
| * The request processor | ||
| * | ||
| */ | ||
| protected final SparqlBasedRequestProcessorForTPFs requestProcessor; | ||
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| @Override | ||
| public IFragmentRequestParser getRequestParser() | ||
| { | ||
| return TPFRequestParserForJenaBackends.getInstance(); | ||
| } | ||
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| @Override | ||
| public IFragmentRequestProcessor getRequestProcessor() | ||
| { | ||
| return requestProcessor; | ||
| } | ||
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| /** | ||
| * Constructor | ||
| * | ||
| * @param title | ||
| * @param description | ||
| */ | ||
| public SparqlDataSource(String title, | ||
| String description, | ||
| URI endpoint, | ||
| String username, | ||
| String password) { | ||
| super(title, description); | ||
| requestProcessor = new SparqlBasedRequestProcessorForTPFs(endpoint, username, password); | ||
| } | ||
| } |
58 changes: 58 additions & 0 deletions
58
src/main/java/org/linkeddatafragments/datasource/sparql/SparqlDataSourceType.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| package org.linkeddatafragments.datasource.sparql; | ||
|
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| import java.net.URI; | ||
| import java.net.URISyntaxException; | ||
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| import org.apache.http.client.utils.URIBuilder; | ||
| import org.linkeddatafragments.datasource.IDataSource; | ||
| import org.linkeddatafragments.datasource.IDataSourceType; | ||
| import org.linkeddatafragments.exceptions.DataSourceCreationException; | ||
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| import com.google.gson.JsonObject; | ||
|
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| /** | ||
| * The type of Triple Pattern Fragment data sources that are backed by | ||
| * a SPARQL endpoint. | ||
| * | ||
| * @author <a href="http://olafhartig.de">Olaf Hartig</a> | ||
| * @author <a href="https://awoods.io">Andrew Woods</a> | ||
| */ | ||
| public class SparqlDataSourceType implements IDataSourceType | ||
| { | ||
| @Override | ||
| public IDataSource createDataSource( final String title, | ||
| final String description, | ||
| final JsonObject settings ) | ||
| throws DataSourceCreationException | ||
| { | ||
| // Required: Set the SPARQL endpoint | ||
| if ( ! settings.has("endpoint")) { | ||
| throw new DataSourceCreationException("SparqlDataSource", "Missing required configuration element: 'endpoint'"); | ||
| } | ||
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| URI endpoint; | ||
| try { | ||
| endpoint = new URIBuilder(settings.getAsJsonPrimitive("endpoint").getAsString()).build(); | ||
| } catch (URISyntaxException e) { | ||
| throw new DataSourceCreationException("SparqlDataSource", "Configuration element, 'endpoint', must be a valid URI"); | ||
| } | ||
|
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| // Set SPARQL endpoint credentials, if provided | ||
| String username = null; | ||
| if (settings.has("username")) { | ||
| username = settings.getAsJsonPrimitive("username").getAsString(); | ||
| } | ||
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| String password = null; | ||
| if (settings.has("password")) { | ||
| password = settings.getAsJsonPrimitive("password").getAsString(); | ||
| } | ||
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| try { | ||
| return new SparqlDataSource(title, description, endpoint, username, password); | ||
| } catch (Exception ex) { | ||
| throw new DataSourceCreationException(ex); | ||
| } | ||
| } | ||
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| } |
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