Query Protocol Issue

Support
1

Hi Stardog Community,

I’m encountering an issue when querying a Stardog SPARQL endpoint and would appreciate your insights or suggestions. Below are the details:

Endpoint:
https://sd-d8db509a.stardog.cloud:5820/JTH-Product-Data

Problem Description

While performing SPARQL queries from different clients and environments, I noticed inconsistent behavior regarding response formats:

  1. Using the SERVICE keyword in GraphDB:
SELECT * WHERE {  
    SERVICE <https://sd-d8db509a.stardog.cloud:5820/JTH-Product-Data> {  
        <http://example.org/fagerhult_notor_product_data#7320046635763> ?property ?value .  
    }  
}

Result:
500: Error Query evaluation error: Unsupported Media Type

  1. Using dotNetRDF's SparqlRemoteEndpoint.QueryWithResultSet method:
SparqlRemoteEndpoint endpoint = new SparqlRemoteEndpoint(new Uri("https://sd-d8db509a.stardog.cloud:5820/JTH-Product-Data"));  
endpoint.Credentials = new System.Net.NetworkCredential("**user**", "**pwd**");  
SparqlResultSet results = endpoint.QueryWithResultSet("SELECT ?property ?value WHERE { <http://example.org/fagerhult_notor_product_data#7320046635763> ?property ?value }");

Result:
Exception: "Unable to Parse a SPARQL Result Set from the provided XML since the Document Element is not a element!"

  1. Using dotNetRDF's SparqlRemoteEndpoint.QueryRaw method:
    Observation:
    The raw HTTP response has a Content-Type header set to text/turtle.

I also tried setting the Accept header explicitly to application/sparql-results+json, but the response format didn’t change and remained text/turtle.

Working Solution

The only method that worked was using the StardogConnector class from dotNetRDF:

StardogConnector connector = new StardogConnector("https://sd-d8db509a.stardog.cloud:5820/JTH-Product-Data", "**user**", "**pwd**");  
SparqlResultSet results = connector.Query("SELECT ?property ?value WHERE { <http://example.org/fagerhult_notor_product_data#7320046635763> ?property ?value }");

Key Question:

According to the SPARQL 1.1 Protocol, the specified response formats for SPARQL queries should include XML, JSON, and CSV/TSV.

Why is Stardog returning text/turtle instead of one of the standard formats?

Is there a way to enforce the response format (e.g., JSON or XML) when querying the endpoint?

Any guidance or suggestions would be greatly appreciated!

Thanks in advance!

Best regards,
Rahel

2

Hi,

That is indeed odd behavior, especially since text/turtle isn't even a valid response type for a SELECT query. Do either of the first two methods work if you add /query to the end of the URL?

Regardless, could you share an example of the text/turtle response that you're getting? My instance is defaulting to application/sparql-results+xml

3

output.ttl (375.3 KB)
Thank you for your response. Attached is the stream returned. Very strange?
The query is "SELECT ?property ?value WHERE {http://example.org/fagerhult_notor_product_data#7320046635763 ?property ?value }"

And the actual request as encoded by dotNetRDF:
"https://sd-d8db509a.stardog.cloud:5820/JTH-Product-Data?query=SELECT+%3Fproperty+%3Fvalue+WHERE+{<http%3A%2F%2Fexample.org%2Ffagerhult_notor_product_data%237320046635763>+%3Fproperty+%3Fvalue+}"

4

Hi,
Thank you for your response. Could you kindly review what @Lars_Wikstrom has written? We are working on the same project and would greatly appreciate your support.

Kind regards,
Rahel

5

As suggest by @Stephen, make sure to add the /query to the endpoint URL.
That is, should be something like:

https://sd-d8db509a.stardog.cloud:5820/JTH-Product-Data/query?query=...

Best regards
Lars

6

Thank you! Now it works fine with the standard sparql calls from dotNetRDF. I still get an error "Query evaluation error: org.eclipse.rdf4j.query.QueryEvaluationException: org.eclipse.rdf4j.query.resultio.QueryResultParseException: File does not contain a binary RDF table result" when trying to query as SERVICE from GraphDB, but I guess that I will have to take that thing with those guys.