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

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

QLever configuration example

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

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1. \n

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

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

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   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).

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2. \n

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

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

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

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   See bearer token authentication for details.

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3. \n

   Uncomment the credentials secret in docker-compose.yml:

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

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4. \n

   Start LinkedDataHub:

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   make up -- --build

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

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

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Troubleshooting

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

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

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Bootstrap fails with HTTP 401 or 403

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

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Queries work but data import fails

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

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Connection refused errors

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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.

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

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