13.1 Data Sources

Data sources are repositories of RDF objects.

A data source can refer to an Oracle database, or to an external RDF service that can be accessed by an endpoint URL such as Dbpedia or Jena Apache Fuseki. The data source can be defined by generic and as well as specific parameters. Some of the generic parameters are name, type, and description. Specific parameters are JDBC properties (for database data sources) and endpoint base URL (for external data sources).

• Oracle Data Sources
  
• Endpoint URL Data Sources
  

13.1.1 Oracle Data Sources

Oracle data sources are defined using JDBC connections. Three types of Oracle JDBC data sources can be defined:

• A JDBC URL data source with standard Oracle JDCB parameters, which include SID or service name, host, port, and user credentials.
• A container JDBC data source that can be defined inside the application Server (WebLogic, Tomcat, or others).
• An Oracle wallet data source that contains the files needed to make the database connection.

The parameters that define an Oracle database data source include:

• name: A generic name of the data source.
• type: The data source type. For databases, it must be ‘DATABASE’.
• description (optional): A generic description of the data source.
• properties: Specific mapping parameters with values for data source properties:
  • For a JDBC URL:
    • Database SID or service name
    • Host machine
    • Database listening port
    • User name and password credentials
  • For a container data source:
    • JNDI name - Java naming and directory interface (JNDI) name
  • For a wallet data source:
    • A string describing the wallet service
    • User name and password credentials (required if the user credentials are not stored in the wallet)
    • Optional proxy details

    For a cloud wallet it is usually an alias name stored in the tnsnames.ora file, but for a simple wallet it contains the host, port, and service name information.

The following example shows the JSON representation of a JDBC URL data source.

{
    "name" : "rdfuser_jdbc_sid",
    "type" : "DATABASE",
    "description" : "",
    "properties" : {
	"host" : "127.0.0.1"	 
	"sid" : "orcl193"
	"port" : "1524",
	"user" : "rdfuser",
        "password" : "<password>"      
    }
}

The following example shows the JSON representation of a container data source:

{
   "name": "rdfuser_ds_ct",
   "type": "DATABASE",
   "description": "Database Container connection",
   "properties": {
       "jndiName": "jdbc/RDFUSER193c"
   }
}

The following example shows the JSON representation of a wallet data source where the credentials are stored in the wallet:

{
   "name": "rdfuser_ds_wallet",
   "type": "DATABASE",
   "description": "Database wallet connection",
   "properties": {
       "walletService": "db202002041627_medium"
   }
}

13.1.2 Endpoint URL Data Sources

External RDF data sources are defined using an endpoint URL. In general, each RDF store has a generic URL that accepts SPARQL queries and SPARQL updates. Depending on the RDF store service, it may also provide some capabilities request to retrieve available datasets.

Table 13-1 External Data source Parameters

Parameters	Description
name	A generic name of the data source.
type	The type of the data source. For external data sources, the type must be ‘ENDPOINT’.
description	A generic description of the data source.
properties	Specific mapping parameters with values for data source properties: base URL: the base URL to issue SPARQL queries to RDF store. This is the default URL. query URL (optional): the URL to execute SPARQL queries. If defined, it will overwrite the base URL value. update URL (optional): the URL to execute SPARQL updates. If defined, it will overwrite the base URL value. capabilities (optional): Some RDF stores (like Apache Jena Fuseki) may provide a capabilities URL that returns the datasets available in service. A JSON response is expected in this case. get URL: the get capabilities URL. datasets parameter: defines the JSON parameter that contains the RDF datasets information. dataset parameter name: defines the JSON parameter that contains the RDF dataset name.

The following example shows the JSON representation of a Dbpedia external data source :

{
  "name": "dbpedia",
  "type": "ENDPOINT",
  "description": "Dbpedia RDF data - Dbpedia.org",
  "properties": {
      "baseUrl": "http://dbpedia.org/sparql",
      "provider": "Dbpedia"
   }
}

The following example shows the JSON representation of a Apache Jena Fuseki external data source. The ${DATASET} is a parameter that is replaced at run time with the Fuseki dataset name:

{
    "name": "Fuseki",
    "type": "ENDPOINT",
    "description": "Jena Fuseki server",
    "properties": {
      "queryUrl": "http://localhost:8080/fuseki/${DATASET}/query",
      "baseUrl": "http://localhost:8080/fuseki",
      "capabilities": {
        "getUrl": "http://localhost:8080/fuseki/$/server",
        "datasetsParam": "datasets",
        "datasetNameParam": "ds.name"
      },
      "provider": "Apache",
      "updateUrl": "http://localhost:8080/fuseki/${DATASET}/update"
    }
}