SPARQL is a query language and a remote access protocol. The remote access protocol can be used with plain HTTP or over SOAP.
See Fuseki for an implementation of the SPARQL protocol over HTTP. Fuseki uses ARQ to provide SPARQL query access to Jena models, including Jena persistent models.
ARQ includes a query engine capable of using the HTTP version.
The QueryExecutionFactory
has methods for creating a
QueryExecution
object for remote use.
QueryExecutionFactory.sparqlService
These methods build a query execution object that uses the query
engine in com.hp.hpl.jena.sparql.engine.http
.
The remote request is made when the execSelect
, execConstruct
,
execDescribe
or execAsk
method is called.
The results are held locally after remote execution and can be processed as usual.
The arq.sparql
command can issue remote
query requests using the --service
argument:
java -cp ... arq.query --service 'http://host/service' 'SELECT ?s WHERE {?s [] []}'
This takes a URL that is the service location.
The query given is parsed locally to check for syntax errors before sending.
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.
If, to use your web browser, you need to set a proxy, you need to do so for a Java program.
Simple examples include:
-DsocksProxyHost=YourSocksServer -DsocksProxyHost=YourSocksServer -DsocksProxyPort=port -Dhttp.proxyHost=WebProxy -Dhttp.proxyPort=Port
This can be done in the application if it is done before any network connection are made:
System.setProperty("socksProxyHost", "socks.corp.com");
Consult the Java documentation for more details. Searching the web is also very helpful.