SPARQL

The SPARQL Web service is used to send custom SPARQL queries against the structWSF data structure. This is a general purpose querying Web service.

Developers communicate with the SPARQL Web service using the HTTP POST method. You may request one of the following mime types: (1) text/xml, (2) application/rdf+xml, (3) application/rdf+n3, (4) application/sparql-results+xml, (5) application/sparql-results+json or (6) application/json. The content returned by the Web service is serialized using the mime type requested and the data returned depends on the parameters selected.

Version
This documentation page is used for the version 2 of this endpoint. Check at the top of this page to see the documentation pages for the other versions of this endpoint.

Usage
This Web service is intended to be used by content management systems, developers or administrators to manage access to WSF (Web Service Framework) resources (users, datasets, Web services endpoints).

If the requested content type sent to the SPARQL web service endpoint is not " " nor " ", then it means that the web service is used to return complete record descriptions based on a SPARQL search pattern. Only the two SPARQL resultsets serialization formats will return the except SPARQL resultsets.

If the SPARQL endpoint is used to get complete records description based on SPARQL patterns, then the three variables (1), (2)   and (3)   variables have to be bound in the SPARQL query, otherwise no result will be returned. Here is an example of a query that match all the records that are muni:County and that have an iron:prefLabel. However, as you can notice in the query, the three variable  are bound so that the SPARQL endpoint return the complete record description for the requested content type " ":

Optionally, the requester can define a fourth variable (4)  to get the dataset location of each returned result in the resultset. This location is defined in the record's description using the  predicate. Here is an example of such a query:

To comply with the SPARQL protocol, the parameters  and   are supported by the endpoint.

When a query is sent to this SPARQL endpoint, the user has to specify the dataset he wants to query, and he has to have access to it. If the dataset URI is not specified, or if he doesn't have access to it, then an error will be reported by the endpoint.

To specify the dataset he wants to send the query against, the user can specify it via the endpoint parameters,   or. Also, he can specify it directly within the SPARQL query via the clauses  and.

Note that any SPARQL queries that uses GRAPH clauses will return a 205 error if the SPARQL query is not bound to one or a set of FROM NAMED clauses. This is the only way to ensure that the user will access the data he has access to. If you are a developer, you may want to use the Auth: Lister Web service endpoint to get all the datasets accessible to the user, and then to put all of them into the SPARQL query using the FROM NAMED clause so that you can use the GRAPH clause within your SPARQL queries.

Finally, any SPARUL queries will be dropped by the endpoint, and a 203 error will be returned to the requester.

Web Service Endpoint Information
This section describes the permissions you need in the WSF (Web Service Framework) to send a query to this Web service endpoint, and it describes how to access it.

To access this Web service endpoint you need the proper CRUD (Create, Read, Update and Delete) permissions on a specific graph (dataset) of the WSF. Without the proper permissions on this graph you won't be able to send any queries to the endpoint.

Needed registered CRUD permission:


 * Create: False
 * Read: True
 * Update: False
 * Delete: False

As shown on the graph URI:


 * URI of the dataset where the instance record is indexed

Here is the information needed to communicate with this Web service's endpoint. Descriptions of the parameters are included below.

Note: if a parameter has a default value, the requester can omit it and the default value will be used. Also, some baseline Web services may not offer other values than the default.

HTTP method:


 * POST

Possible "Accept:" HTTP header field values:


 * text/xml (structXML)
 * application/json (structJSON)
 * application/rdf+xml (RDF+XML)
 * application/rdf+n3 (N3/Turtle)
 * application/iron+json (irJSON)
 * application/iron+csv (commON)
 * application/sparql-results+xml (SPARQL resultset in XML)
 * application/sparql-results+json (SPARQL resultset in JSON)

Possible "Accept:" HTTP header field values for a DESCRIBE or a CONSTRUCT SPARQL query:


 * text/rdf+n3 (RDF+N3)
 * application/rdf+xml (RDF+XML)
 * application/rdf+json (RDF+JSON)
 * text/plain (NTRIPLES)

URI:


 * http://[...]/ws/sparql/ ?query=param1&dataset=param2&limit=param3&offset=param4&registered_ip=param5&default-graph-uri=param6&named-graph-uri=param7&interface=param8

URI dynamic parameters description:

Note: All parameters have to be URL-encoded


 * param1. The SPARQL query to send to the Web service endpoint
 * param2. URI referring to a target dataset to query.
 * param3. Limit of the number of results to return in the resultset(max 2000)
 * param4. Offset of the "sub-resultset" from the total resultset of the query
 * param5. Target IP address registered in the WSF. Needed when the IP of the requester is not the one of the one making the request to the endpoint. Otherwise this parameter as to be omitted.
 * param6. Dataset to target with the sparql query (optional) -- only used for consistency with the SPARQL protocol
 * param7. Dataset to target with the sparql query (optional) -- only used for consistency with the SPARQL protocol
 * param8. Source interface used for this web service query. The interface is a different way to process a query (different algorithms, different data management system, etc. The default interface is 'default'

Available Sources Interfaces
A source interface is a way to process a web service query. Different sources interfaces can be implemented for the same structWSF web service endpoint. Each interface will process the query differently, but all the queries to the web service endpoint will be the same, at the exception of the  parameter. Each interface shares the same API (the one defined by the web service endpoint), but their processing may differ (like using different algorithms, using different data management systems, etc.)

This is a list of the core interfaces for this endpoint. Organizations that hosts a structWSF network could create their own interface and make it available to the users. However such private source interface won't be part of this list, but should be publicized by the organization.

Content Returned
The content returned by the Web service endpoint depends on the "Accept:" parameter sent by the requester. The user can request one of the five supported mime types. The converted content from the input document will be returned by using the requested serialization format.

HTTP Status Codes
Here are the possible HTTP status (error) codes returned by this Web service endpoint.

On error code and the specific error, a different message description can be issued (meaning a different error has been returned).


 * Code:200
 * Message:OK


 * Code:400
 * Message:Bad Request
 * Message description:No query specified for this request
 * Message description:No dataset specified for this request
 * Message description:No data to import
 * Message description:No requester IP available
 * Message description:No Web service URI available
 * Message description:GRAPH not permitted. The SPARQL GRAPH clause is not permitted for this sparql endpoint. Please change your SPARQL query to specify the datasets you want to query with the FROM and FROM NAMED sparql clauses, or with the dataset parameter.
 * Message description:SPARUL not permitted. No SPARUL queries are permitted for this sparql endpoint.
 * Message description:Target Web service XYZ not registered to this Web Services Framework
 * Message description:No access defined for this requester IP XYZ, dataset (XYZ) and Web service (XYZ)
 * Message description:The target Web service (XYZ) needs create access and the requested user (XYZ) doesn't have this access for that dataset (XYZ)
 * Message description:The target Web service (XYZ) needs read access and the requested user (XYZ) doesn't have this access for that dataset (XYZ)
 * Message description:The target Web service (XYZ) needs update access and the requested user (XYZ) doesn't have this access for that dataset (XYZ)
 * Message description:The target Web service (XYZ) needs delete access and the requested user (XYZ) doesn't have this access for that dataset (XYZ)


 * Code:406
 * Message:Not Acceptable
 * Message description:Unacceptable mime type requested


 * Code:500
 * Message:Internal Error