A hydra-count rdf-metadata-extract actor

Usage no npm install needed!

<script type="module">
  import comunicaActorRdfMetadataExtractHydraCount from 'https://cdn.skypack.dev/@comunica/actor-rdf-metadata-extract-hydra-count';


Comunica Hydra Count RDF Metadata Extract Actor

npm version

An RDF Metadata Extract actor that extract estimated counts in the Hydra Core vocabulary and VoID.

This module is part of the Comunica framework, and should only be used by developers that want to build their own query engine.

Click here if you just want to query with Comunica.


$ yarn add @comunica/actor-rdf-metadata-extract-hydra-count

Metadata entries

This actor adds the following entries to the metadata object.

  • cardinality: Value of http://www.w3.org/ns/hydra/core#totalItems or http://rdfs.org/ns/void#triples represented as { type: 'exact' | 'estimate', value: number }.


After installing, this package can be added to your engine's configuration as follows:

  "@context": [
  "actors": [
      "@id": "urn:comunica:default:rdf-metadata-extract/actors#hydra-count",
      "@type": "ActorRdfMetadataExtractHydraCount",
      "predicates": [

Config Parameters

  • predicate: The predicates to consider when determining counts, defaults to http://www.w3.org/ns/hydra/core#totalItems and http://rdfs.org/ns/void#triples.