@comunica/actor-init-sparql-rdfjs

A SPARQL query engine for querying over RDF/JS sources

Usage no npm install needed!

<script type="module">
  import comunicaActorInitSparqlRdfjs from 'https://cdn.skypack.dev/@comunica/actor-init-sparql-rdfjs';
</script>

README

Comunica SPARQL RDFJS Init Actor

npm version

Comunica SPARQL is a SPARQL query engine for JavaScript for querying RDFJS sources that implement the Source interface.

This module is part of the Comunica framework.

Install

$ yarn add @comunica/actor-init-sparql-rdfjs

Query

const newEngine = require('@comunica/actor-init-sparql-rdfjs').newEngine;
const N3Store = require('n3').Store;
const DataFactory = require('n3').DataFactory;

// This can be any RDFJS source
const store = new N3Store();
store.addQuad(DataFactory.quad(
  DataFactory.namedNode('a'), DataFactory.namedNode('b'), DataFactory.namedNode('http://dbpedia.org/resource/Belgium')));
store.addQuad(DataFactory.quad(
  DataFactory.namedNode('a'), DataFactory.namedNode('b'), DataFactory.namedNode('http://dbpedia.org/resource/Ghent')));

// Create our engine, and query it.
// If you intend to query multiple times, be sure to cache your engine for optimal performance.
const myEngine = newEngine();
const result = await myEngine.query('SELECT * { ?s ?p <http://dbpedia.org/resource/Belgium>. ?s ?p ?o } LIMIT 100',
  { sources: [store] });
result.bindingsStream.on('data', (data) => {
  // Each data object contains a mapping from variables to RDFJS terms.
  console.log(data.get('?s'));
  console.log(data.get('?p'));
  console.log(data.get('?o'));
});

Read more about querying in an application.

Update

const newEngine = require('@comunica/actor-init-sparql-rdfjs').newEngine;
const N3Store = require('n3').Store;

// This can be any RDFJS store
const store = new N3Store();

// Create our engine, and query it.
const myEngine = newEngine();
const query = `
PREFIX dc: <http://purl.org/dc/elements/1.1/>
INSERT DATA
{ 
  <http://example/book1> dc:title "A new book" ;
                         dc:creator "A.N.Other" .
}
`;

// Initiate the update
const result = await myEngine.query(query, {
  sources: [store],
});

// Wait for the update to complete
await result.updateResult;

// Prints '2' => the store is updated
console.log(store.size);

Read more about updating in an application.

Optimization

The RDFJS Source interface by default only exposed the match method. In order to allow Comunica to produce more efficient query plans, you can optionally expose a countQuads method that has the same signature as match, but returns a number or Promise<number> that represents (an estimate of) the number of quads that would match the given quad pattern. Certain Source implementations may be able to provide an efficient implementation of this method, which would lead to better query performance.

If Comunica does not detect a countQuads method, it will fallback to a sub-optimal counting mechanism where match will be called again to manually count the number of matches.