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SPARQL API

This chapter is for software developers building applications, dashboards or harvesters on top of the Dataset Register, and for researchers who want to find datasets across the Dutch heritage network by querying its metadata directly. It gives a high-level overview of the endpoint, what you can do with it, and how it relates to the data model; it intentionally does not repeat the full vocabulary reference.

The SPARQL endpoint exposes the entire contents of the Register: every registered dataset description, its registration metadata, and the validation status of the URLs it was fetched from. Use the REST API to change the Register; use SPARQL to read from it.

Endpoint​

The SPARQL endpoint URL is:

https://datasetregister.netwerkdigitaalerfgoed.nl/sparql

For a query web interface, use the QLever web interface.

Or query from the command-line, for example using the Comunica SPARQL client:

comunica-sparql sparql@https://datasetregister.netwerkdigitaalerfgoed.nl/sparql \
  'select * { ?s a <http://www.w3.org/ns/dcat#Dataset> ; ?p ?o . } limit 100'

Or cURL:

curl -H 'Accept: application/sparql-results+json' \
  --data-urlencode 'query=select * { ?s a <http://www.w3.org/ns/dcat#Dataset> ; ?p ?o . } limit 100' \
  https://datasetregister.netwerkdigitaalerfgoed.nl/sparql

Data model​

The endpoint exposes dataset descriptions in DCAT. The data model chapter is the authoritative reference on every class and property you can query; jump straight to the section you need:

  • Dataset: dcat:Dataset, dcat:Distribution, foaf:Agent
  • Registration: the register-specific metadata used for registration status below
  • Distribution health: per-URL probe results (reachability and content-type match), exposed in a dedicated named graph
  • SHACL validation report: the full validation report per registration, in a dedicated named graph; the warning count is summarised on the registration as nde:warningCount
  • Allow list: which domains are permitted to register datasets

Registration status​

In addition to the dataset description itself, the Register stores metadata about how it was registered: the registration URL it was fetched from, the timestamp of the latest fetch, and whether that fetch produced a valid description. Most useful applications want to filter on status – for example, only show currently valid datasets, or only datasets that have been re-validated recently.

The full set of properties on a registration is documented under schema:EntryPoint (the registration URL itself) and schema:Dataset (each dataset found at that URL). For filtering on validity, each dataset links back to its registration URL via schema:subjectOf, and the registration URL carries a schema:additionalType flag indicating its current status:

PREFIX dcat: <http://www.w3.org/ns/dcat#>
PREFIX schema: <https://schema.org/>
SELECT * {
  ?dataset a dcat:Dataset ;
    schema:subjectOf ?registrationUrl .
  ?registrationUrl schema:additionalType <https://data.netwerkdigitaalerfgoed.nl/registry/valid>
}

You can try this in the QLever web interface.

Building queries​

The Dataset Register website offers a ‘SPARQL’ button on each dataset that produces a starter query for the dataset’s predicates – a useful way to see real-world property usage before writing your own queries.

For broader exploration, the data model chapter is the better starting point: it documents every property the Register exposes, with the same cardinalities and tags that appear in the data.