@comunica/query-sparql-rdfjs-lite
v4.0.2
Published
A lightweight SPARQL query engine for querying over RDF/JS sources
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Comunica SPARQL RDF/JS Lite
Comunica SPARQL is a SPARQL query engine for JavaScript for querying RDF/JS sources that implement the Source interface.
This package has been optimized for a small bundle size when it is used in Web applications. At the time of writing, the minified size of this package is 648,88 KB (145,79 KB when gzipped).
This package excludes the ability to query external SPARQL endpoints via the SERVICE
keyword,
and does not allow serialization of results to formats such as SPARQL/JSON and SPARQL/XML.
If such functionality would be needed, Comunica SPARQL RDF/JS
should be used instead.
This module is part of the Comunica framework.
Install
$ yarn add @comunica/query-sparql-rdfjs-lite
Query
const QueryEngine = require('@comunica/query-sparql-rdfjs-lite').QueryEngine;
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 = new QueryEngine();
const bindingsStream = await myEngine.queryBindings(`
SELECT ?s ?p ?o WHERE {
?s ?p <http://dbpedia.org/resource/Belgium>.
?s ?p ?o
} LIMIT 100`, {
sources: [store],
});
// Consume results as a stream (best performance)
bindingsStream.on('data', (binding) => {
console.log(binding.toString()); // Quick way to print bindings for testing
console.log(binding.has('s')); // Will be true
// Obtaining values
console.log(binding.get('s').value);
console.log(binding.get('s').termType);
console.log(binding.get('p').value);
console.log(binding.get('o').value);
});
bindingsStream.on('end', () => {
// The data-listener will not be called anymore once we get here.
});
bindingsStream.on('error', (error) => {
console.error(error);
});
// Consume results as async iterable (easier)
for await (const binding of bindingsStream) {
console.log(binding.toString());
}
// Consume results as an array (easier)
const bindings = await bindingsStream.toArray();
console.log(bindings[0].get('s').value);
console.log(bindings[0].get('s').termType);
Read more about querying in an application.
Update
const QueryEngine = require('@comunica/query-sparql-rdfjs-lite').QueryEngine;
const N3Store = require('n3').Store;
// This can be any RDFJS store
const store = new N3Store();
// Create our engine, and query it.
const myEngine = new QueryEngine();
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" .
}
`;
// Execute the update
await myEngine.queryVoid(query, {
sources: [store],
});
// 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.