Requirements

For a triplestore to work with LinkedDataHub, it must support the following:

Service configuration

Services are configured in config/system.trig using three key properties. See the dataspace reference for the full list of service properties and the default Fuseki service declaration — the configuration you start with. The sections below walk through configuring an alternative backend (QLever) instead.

Authentication

LinkedDataHub supports two authentication methods for SPARQL services, both configured in secrets/credentials.trig. The file is mounted as a Docker secret and is not committed to version control (the /secrets folder is gitignored). See the configuration reference for the credentials secret entry.

@prefix a: <https://w3id.org/atomgraph/core#> .

<urn:linkeddatahub:services/end-user>
{
    <urn:linkeddatahub:services/end-user> a:authUser "username" ;
        a:authPwd "password" .
}

<urn:linkeddatahub:services/admin>
{
    <urn:linkeddatahub:services/admin> a:authUser "username" ;
        a:authPwd "password" .
}

@prefix a: <https://w3id.org/atomgraph/core#> .

<urn:linkeddatahub:services/end-user>
{
    <urn:linkeddatahub:services/end-user> a:authToken "your-bearer-token" .
}

<urn:linkeddatahub:services/admin>
{
    <urn:linkeddatahub:services/admin> a:authToken "your-bearer-token" .
}

QLever configuration example

QLever is a high-performance triplestore optimized for text search. To configure LinkedDataHub to use QLever:

1. Update config/system.trig to point to your QLever instance:

   @prefix lds: <https://w3id.org/atomgraph/linkeddatahub/dataspaces#> .
   @prefix a:    <https://w3id.org/atomgraph/core#> .
   @prefix sd:   <http://www.w3.org/ns/sparql-service-description#> .
   @prefix dct:  <http://purl.org/dc/terms/> .
   
   # Admin app: type and service binding
   
   <urn:linkeddatahub:apps/admin>
   {
       <urn:linkeddatahub:apps/admin> a lds:AdminDataspace ;
           lds:service <urn:linkeddatahub:services/admin> .
   }
   
   # Admin service: QLever
   
   <urn:linkeddatahub:services/admin>
   {
       <urn:linkeddatahub:services/admin> a sd:Service ;
           dct:title "LinkedDataHub admin service (QLever)" ;
           sd:supportedLanguage sd:SPARQL11Query, sd:SPARQL11Update ;
           sd:endpoint <http://qlever-host:7001/> ;
           # a:quadStore omitted: QLever uses GSP fallback mode
           a:graphStore <http://qlever-host:7001/> .
   }
   
   # End-user app: type and service binding
   
   <urn:linkeddatahub:apps/end-user>
   {
       <urn:linkeddatahub:apps/end-user> a lds:EndUserDataspace ;
           lds:service <urn:linkeddatahub:services/end-user> .
   }
   
   # End-user service: QLever
   
   <urn:linkeddatahub:services/end-user>
   {
       <urn:linkeddatahub:services/end-user> a sd:Service ;
           dct:title "LinkedDataHub service (QLever)" ;
           sd:supportedLanguage sd:SPARQL11Query, sd:SPARQL11Update ;
           sd:endpoint <http://qlever-host:7001/> ;
           # a:quadStore omitted: QLever uses GSP fallback mode
           a:graphStore <http://qlever-host:7001/> .
   }

   content_copy

   The a:quadStore property is omitted because QLever does not support dataset-level TriG/N-Quads uploads. LinkedDataHub will automatically fall back to using graph-scoped Graph Store Protocol operations (see service configuration).

2. Configure Bearer token authentication (QLever requires this for write operations):

   Create secrets/credentials.trig with your QLever access token:

   @prefix a: <https://w3id.org/atomgraph/core#> .
   
   <urn:linkeddatahub:services/end-user>
   {
       <urn:linkeddatahub:services/end-user> a:authToken "your-qlever-bearer-token" .
   }
   
   <urn:linkeddatahub:services/admin>
   {
       <urn:linkeddatahub:services/admin> a:authToken "your-qlever-bearer-token" .
   }

   content_copy

   See bearer token authentication for details.

3. Uncomment the credentials secret in docker-compose.yml:

   services:
     linkeddatahub:
       secrets:
         # ... other secrets ...
         # - credentials  # uncomment this line

   content_copy

4. Start LinkedDataHub:

   make up -- --build

   content_copy

   The -- makes make forward the flags that follow it to docker-compose.

   During bootstrap, LinkedDataHub will load the default datasets using graph-scoped GSP operations. This takes longer than quad store mode but is functionally equivalent.

Troubleshooting

Bootstrap fails with HTTP 400 "application/trig not supported"

Your triplestore does not support dataset-level uploads. Remove the a:quadStore property from your service configuration to use GSP fallback mode.

Bootstrap fails with HTTP 401 or 403

Check your authentication configuration. Both Bearer token and HTTP Basic auth are configured in secrets/credentials.trig. See authentication for details.

Queries work but data import fails

Ensure your triplestore supports SPARQL 1.1 Update and Graph Store Protocol, not just Query. Check the triplestore requirements.

Connection refused errors

Check that the endpoint URLs are reachable from the LinkedDataHub Docker container. If running QLever in Kubernetes, use port-forwarding or set up proper networking.

For background discussion of the QLever integration, see GitHub issue #272.

Browse available triplestore products at kgdev.net/products/.