arq-1application api

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1、ARQ-ApplicationAPITheapplicationAPIisinthepackagecom.hp.hpl.jena.query.Otherpackagescontainvariouspartsofthesystem(executionengine,parsers,testingetc).Mostapplicationswillonlyneedtousethemainpackage.Onlyapplicationswishingtoprogrammaticallybuildqueriesormodifythebehaviourofthequeryengineneedtouset

2、heotherspackagesdirectly.KeyClassesThepackagecom.hp.hpl.jena.queryisthemainapplicationpackage.Query-aclassthatrepresentstheapplicationquery.Itisacontainerforallthedetailsofthequery.ObjectsofclassQueryarenormallycreatedbycallingoneofthemethodsofQueryFactorymethodswhichprovideaccesstothevariouspars

3、ers.QueryExecution-representsoneexecutionofaquery.QueryExecutionFactory-aplacetogetQueryExecutioninstancesDatasetFactory-aplacetomakedatasets,includingmakingaDataSource(anupdatableDataset)ForSELECTqueries:QuerySolution-AsinglesolutiontothequeryResultSet-AlltheQuerySolutions.Aniterator.Resul

4、tSetFormatter-turnaResultSetintovariousforms;intotext,intoanRDFgraph(Model,inJenaterminology)orasplainXMLSELECTqueriesThebasicstepsinmakingaSELECTqueryareoutlinedintheexamplebelow.AqueryiscreatedfromastringusingtheQueryFactory.ThequeryandmodelorRDFdatasettobequeriedarethenpassedtoQueryExecutionFac

5、torytoproduceaninstanceofaqueryexecution.Resultarehandledinaloopandfinallythequeryexecutionisclosed.importcom.hp.hpl.jena.query.*;Modelmodel=...;StringqueryString="....";Queryquery=QueryFactory.create(queryString);QueryExecutionqexec=QueryExecutionFactory.create(query,model);try{ResultSetresults=q

6、exec.execSelect();for(;results.hasNext();){QuerySolutionsoln=results.nextSolution();RDFNodex=soln.get("varName");//Getaresultvariablebyname.Resourcer=soln.getResource("VarR");//Getaresultvariable-mustbearesourceLiterall=soln.getLiteral("VarL");//Getaresultvariable-mustbealiteral}}finally{qexec.clo

7、se();}Itisimportanttocleanlyclosethequeryexecutionwhenfinished.Systemresourcesconnectedtopersistentstoragemayneedtobereleased.AResultSetARQsupportstheJavaiteratorinterfacesothefollowingisalsoawaytoprocesstheresul