Virtuoso Redland RDF Storage Provider

What is Redland

Redland is a set of free software 'C' libraries that provide support for the Resource Description Framework (RDF), providing modular, object based libraries and APIs for manipulating the RDF graph, triples, URIs and Literals. Redland includes several high-level language APIs providing RDF manipulation and storage and requires the Raptor RDF parser and Rasqal RDF syntax and query library for its use.

What is the Virtuoso Redland Provider

The Virtuoso Redland RDF Provider is an implementation of the Storage API, Model and Query interfaces of the Redland framework for RDF. This provider enables the execution of queries via the Redland Rasqal query engine or via Virtuoso query engine directly against the Virtuoso Quad store. The Virtuoso Redland Provider uses ODBC as the data access mechanism for communicating the Virtuoso Quad Store and requires the Virtuoso ODBC Driver be installed on the Redland client and a suitable ODBC DSN be configured for connecting to the target Virtuoso Quad Store instance. The provider has been tested against the Redland 1.0.8 version available for download at the time.

Fig 1 Redland Component Stack

As indicated in the above diagram the Virtuoso Provider can be used to execute RDF queries either directly against the Virtuoso graph storage module supporting the SPARQL, SPARUL, SPARQL-BI query languages or via the Rasqal query engine built into Redland which supports the SPARQL query language. This is done by simply changing the syntax of the query using the "vsparql" rather then default "sparql" construct when executing a query as indicated in the sample queries below:

rdfproc -r xml -t "user='dba',password='dba',dsn='Demo'" gr query sparql - "SELECT * WHERE { ?s ?p ?o }"            ;; via Redland Rasqal engine

rdfproc -r xml -t "user='dba',password='dba',dsn='Demo'" gr query vsparql - "SELECT * WHERE { ?s ?p ?o }"          ;; direct to Virtuoso storage module

The Virtuoso Provider uses the SPASQL query language for querying the remote Virtuoso QUAD store.


Required files

The Virtuoso Redland Provider has been integrated into the Redland RDF Framework and submitted to the open source project to become part of the standard distribution available for download.

Compling Redland with Virtuoso storage support

Connection Parameters

The Virtuoso provider has the following connection parameters available fro use:

NOTE: Take care exposing the password as for example, program arguments or environment variables. The rdfproc utility can help this by reading the password from standard input. Inside programs, one way to prevent storing the password in a string is to construct a Redland hash of the storage options such as via librdf hash_from_string and use librdf_new_storage_with_options to create a storage. The rdfproc utility source code demonstrates this.

The storage name parameter given to the storage constructor librdf new_storage is used inside the virtuoso store to allow multiple stores inside one Virtuoso database instance as parameterised with the above options.

This store always provides contexts; the boolean storage option contexts is not checked.


  /* A new Virtuoso store */
  storage=librdf_new_storage(world, "virtuoso", "db1",
      "dsn='Local Virtuoso',user='demo',password='demo'");

  /* A different, existing Virtuoso store in the same database as above */
  storage=librdf_new_storage(world, "virtuoso", "db2",
      "dsn='Local Virtuoso',user='demo',password='demo'");

  /* An existing Virtuoso store on a different database server */
  storage=librdf_new_storage(world, "virtuoso", "http://red3",
      "dsn='Remote Virtuoso',user='demo',password='demo'");

  /* Opening with an options hash */
  options=librdf_new_hash(world, NULL);
      "dsn='Local Virtuoso',user='demo'");
  librdf_hash_put_strings(options, "password", user_password);
  storage=librdf_new_storage_with_options(world, "virtuoso", "http://red3", options);


CategoryRDF CategoryOpenSource CategoryVirtuoso CategoryVOS CategoryNativeRDFProviders CategoryDocumentation