Triplestores

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.

sd:endpoint

The SPARQL Protocol endpoint URI (for SPARQL Query and Update operations)

Example: <http://qlever-host:7001/>

a:graphStore

The Graph Store Protocol endpoint URI (for graph-scoped CRUD operations)

Example: <http://qlever-host:7001/>

Required for all triplestores

a:quadStore

The quad store endpoint URI (for dataset-level CRUD operations)

Optional — if omitted, LinkedDataHub will use graph-scoped GSP fallback

Example: <http://fuseki-host:3030/ds/> (Fuseki-specific)

Authentication

LinkedDataHub supports two authentication methods for SPARQL services, both configured in secrets/credentials.trig. 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. Here's how to configure LinkedDataHub to use QLever:

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

   @prefix lapp: <https://w3id.org/atomgraph/linkeddatahub/apps#> .
   @prefix a:    <https://w3id.org/atomgraph/core#> .
   @prefix ldt:  <https://www.w3.org/ns/ldt#> .
   @prefix sd:   <http://www.w3.org/ns/sparql-service-description#> .
   @prefix dct:  <http://purl.org/dc/terms/> .
   
   # Admin app - type + service binding
   
   <urn:linkeddatahub:apps/admin>
   {
       <urn:linkeddatahub:apps/admin> a lapp:AdminApplication ;
           ldt: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:graphStore <http://qlever-host:7001/> .
           # Note: a:quadStore omitted - QLever uses GSP fallback mode
   }
   
   # End-user app - type + service binding
   
   <urn:linkeddatahub:apps/end-user>
   {
       <urn:linkeddatahub:apps/end-user> a lapp:EndUserApplication ;
           ldt: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:graphStore <http://qlever-host:7001/> .
           # Note: a:quadStore omitted - QLever uses GSP fallback mode
   }

   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" .
   }

   See bearer token authentication for details.

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

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

4. Start LinkedDataHub:

   docker-compose up --build

   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 doesn't 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 more details, see GitHub issue #272 which documents the QLever integration process.