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| <h1 class="title">ARQ - Querying Remote SPARQL Services</h1> |
| |
| <p>SPARQL is a |
| <a href="http://www.w3.org/TR/sparql11-query/">query language</a> and a |
| <a href="http://www.w3.org/2001/sw/DataAccess/proto-wd/">remote access protocol</a>. |
| The remote access protocol runs over HTTP.</p> |
| <p>See <a href="../fuseki2/index.html">Fuseki</a> for an implementation of the |
| SPARQL protocol over HTTP. Fuseki uses ARQ to provide SPARQL |
| query access to Jena models, including Jena persistent models.</p> |
| <p>ARQ includes a query engine capable of using the HTTP version.</p> |
| <h2 id="from-your-application">From your application</h2> |
| <p>The <code>QueryExecutionHTTP</code> has methods for creating a |
| <code>QueryExecution</code> object for remote use. There are various |
| HTTP specific settings; the default should work in most cases.</p> |
| <p>The remote request is made when the <code>execSelect</code>, <code>execConstruct</code>, |
| <code>execDescribe</code> or <code>execAsk</code> method is called.</p> |
| <p>The results are held locally after remote execution and can be |
| processed as usual.</p> |
| <h2 id="from-the-command-line">From the command line</h2> |
| <p>The <a href="cmds.html#arq.sparql"><code>arq.sparql</code> command</a> can issue remote |
| query requests using the <code>--service</code> argument:</p> |
| <pre><code>java -cp ... arq.query --service 'http://host/service' 'SELECT ?s WHERE {?s [] []}' |
| </code></pre> |
| <p>This takes a URL that is the service location.</p> |
| <p>The query given is parsed locally to check for syntax errors before |
| sending.</p> |
| <h2 id="authentication">Authentication</h2> |
| <p>ARQ provides a flexible API for authenticating against remote services, see the <a href="../sparql-apis/http-auth.html">HTTP Authentication</a> documentation for more details.</p> |
| <h2 id="firewalls-and-proxies">Firewalls and Proxies</h2> |
| <p>Don’t forget to set the proxy for Java if you are accessing a |
| public server from behind a blocking firewall. Most home firewalls |
| do not block outgoing requests; many corporate firewalls do block |
| outgoing requests.</p> |
| <p>If, to use your web browser, you need to set a proxy, you need to |
| do so for a Java program.</p> |
| <p>Simple examples include:</p> |
| <pre><code>-DsocksProxyHost=YourSocksServer |
| |
| -DsocksProxyHost=YourSocksServer -DsocksProxyPort=port |
| |
| -Dhttp.proxyHost=WebProxy -Dhttp.proxyPort=Port |
| </code></pre> |
| <p>This can be done in the application |
| <em>if it is done before any network connection are made</em>:</p> |
| <pre><code> System.setProperty("socksProxyHost", "socks.corp.com"); |
| </code></pre> |
| <p>Consult the Java documentation for more details. Searching the web |
| is also very helpful.</p> |
| <p><a href="index.html">ARQ documentation index</a></p> |
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