Follow the instructions below to create a data service using a RDF (Resource Description Framework) as the data source.
1. Log on to the product's management console and select "Data Service -> Create" under the "Main" menu.
2. The "Create Data Service" page appears. Fill in the fields and click "Next" . The Data Service name is mandatory.
For more information on advanced configurations, refer to Advanced Data Service Configurations.
3. The "Data Sources" page appears. Click on the "Add New Data Source" link and add your Data Source details. Select the data source type as RDF. For example,
We use a sample resource hosted online but you can also use one in your local machine. The RDF resource used in this example is hosted by NASA in this URL: http://nasa.dataincubator.org/~search.rdf?query=all
Click "Save" .
4. The added data source page appears. You can edit or delete the Data Source. To proceed click "Next ".
5. The "Queries" page appears. Initially your service does not include any queries. Click "Add New Query" to add a new query, input/output mappings, events etc. to your Data Service. Enter query details according to the structure of the response you want.
In this example, we have used the following SPARQL query to extract the specific aircraft information from the data source.
PREFIX space: <http://purl.org/net/schemas/space/>
PREFIX relevance: <http://a9.com/-/opensearch/extensions/relevance/1.0/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
SELECT ?homepage ?name ?alternateName ?internationalDesignator ?mass ?score ?launch ?agency ?description
WHERE {
?craft foaf:homepage ?homepage.
?craft foaf:name ?name.
?craft space:alternateName ?alternateName.
?craft space:internationalDesignator ?internationalDesignator.
?craft space:mass ?mass.
?craft relevance:score ?score.
?craft space:launch ?launch.
?craft space:agency ?agency.
?craft dc:description ?description.
}
The input mapping section is used to specify parameters to the query. The above query extracts aircraft information according to the agency. Therefore, we take agency as an input parameter. Input parameters can be added by clicking "Add Input Mappings" .
We have also used the "Grouped By Element" , "Row Name" and "Row namespace" .
Click on "Add Output Mappings" to map the response to an output XML. Once you have entered the output mapping details, click on "Main Configuration" and then the "Save" button.
The output mappings:
For information on adding validations to your input mappings in the query, refer to section Input Validators . Also, detailed information on writing queries can be found in section Data Service Queries.
6. You have added one query to your data service configuration. You can edit or delete your query. To continue, click "Next" .
7. The "Operations" page appear s. Click the "Add new operation" link to c reate an operation. Select a query to be executed when this operation is called.
Click "Save" once done. For example,
8. The Data Service configuration is done. Click "Finish" . ( You can continue to add resources by clicking the "Next" button if you like.)
9. You will be navigated to the "Deployed services" page .
From here, you can manage your data service. For instructions, refer to section "Service Management."
Exposing Relational Data in RDF Format
The data services feature supports exposing relational data in RDF (Resource Description Framework) format as a service. In the following example, we demonstrate how a CSV data source can be exposed as a RDF resource.
In order to expose relational data in RDF format, you need to configure the relevant data service query accordingly. To start, add a new query to your CSV data service. For instructions on creating a CSV data service, refer to section CSV .
1. Log on to the product's m anagement console and select "Services -> List" under the "Main" menu.
2. The "Deployed Services" page appears which lists out all the currently active services and service groups.
Click on the data service you want to edit.
3. The dashboard of the data service opens. Click on the "Edit Data Service" link. In this example, we edit using the management console.
4. Navigate to the "Queries" page of the data service and click the "Add New Query" link .
5. The "Add New Query" page opens. Since the output is a RDF result set, select output type as RDF from the drop-down list in the "Output Mapping" section.
"RDF Base URI" contains the format of rdf:about URI which uniquely identifies each resource. In this example, the "RDF base URI" takes the value of column 1 of the CSV for each row and replaces it with the RDF about attribute inside rdf:Description element.
RDF Base URI : http://www.product/cd/{1}
Row namespace : http://www.product/cd#
6. To generate the response in RDF format, click the "Add New Output Mapping" link. The "Add/Edit Output Mapping" window opens.
There are two mapping types in RDF Output mapping.
- as an element
- as a resource
When mapping an element as a resource, you need to give the resource URI along with the column name which needs to be mapped in curly brackets as shown below. This way we can link two RDF resources together and create a relationship between the two.
7. Once you create the output mappings, go back to the main configuration and save your RDF query.
8. Once the query is completed, navigate to the resources window by clicking "Next". Detailed information on writing queries can be found in section Data Service Queries.
In the "Resources" window, click "Add New Resource" .
9. To create the RDF resource, you need to map your RDF query as a resource in the data service.
Provide a suitable name and description for your resource. The resource method is Get . Select the the rdfQuery created in the previous step as the Query ID. Click "Finish" to deploy the data service.
Once we create the resource we can access our RDF resource via a rest call.
You can validate generated RDF response by using an Online validator such as: http://www.w3.org/RDF/Validator. For example:
