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Lightning fast, asynchronous, streaming RDF for JavaScript

Build Status Coverage Status npm version DOI

The N3.js library is an implementation of the RDF.js low-level specification that lets you handle RDF in JavaScript easily. It offers:

Parsing and writing is:

Installation

For Node.js, N3.js comes as an npm package.

$ npm install n3
const N3 = require('n3');

N3.js seamlessly works in browsers via webpack or browserify.

Creating triples/quads

N3.js follows the RDF.js low-level specification.

N3.DataFactory will give you the factory functions to create triples and quads:

const { DataFactory } = N3;
const { namedNode, literal, defaultGraph, quad } = DataFactory;
const myQuad = quad(
  namedNode('https://ruben.verborgh.org/profile/#me'),
  namedNode('http://xmlns.com/foaf/0.1/givenName'),
  literal('Ruben', 'en'),
  defaultGraph(),
);
console.log(myQuad.subject.value);         // https://ruben.verborgh.org/profile/#me
console.log(myQuad.object.value);          // Ruben
console.log(myQuad.object.datatype.value); // http://www.w3.org/1999/02/22-rdf-syntax-ns#langString
console.log(myQuad.object.language);       // en

In the rest of this document, we will treat “triples” and “quads” equally: we assume that a quad is simply a triple in a named or default graph.

Parsing

From an RDF document to quads

N3.Parser transforms Turtle, TriG, N-Triples, or N-Quads document into quads through a callback:

const parser = new N3.Parser();
parser.parse(
  `PREFIX c: <http://example.org/cartoons#>
   c:Tom a c:Cat.
   c:Jerry a c:Mouse;
           c:smarterThan c:Tom.`,
  (error, quad, prefixes) => {
    if (quad)
      console.log(quad);
    else
      console.log("# That's all, folks!", prefixes);
  });

The callback's first argument is an optional error value, the second is a quad. If there are no more quads, the callback is invoked one last time with null for quad and a hash of prefixes as third argument.
Pass a second callback to parse to retrieve prefixes as they are read.
If no callbacks are provided, parsing happens synchronously.

By default, N3.Parser parses a permissive superset of Turtle, TriG, N-Triples, and N-Quads.
For strict compatibility with any of those languages, pass a format argument upon creation:

const parser1 = N3.Parser({ format: 'N-Triples' });
const parser2 = N3.Parser({ format: 'application/trig' });

Notation3 (N3) is supported only through the format argument:

const parser3 = N3.Parser({ format: 'N3' });
const parser4 = N3.Parser({ format: 'Notation3' });
const parser5 = N3.Parser({ format: 'text/n3' });

From an RDF stream to quads

N3.Parser can parse Node.js streams as they grow, returning quads as soon as they're ready.

const parser = N3.Parser(),
      rdfStream = fs.createReadStream('cartoons.ttl');
parser.parse(rdfStream, console.log);

N3.StreamParser is a Node.js stream and RDF.js Sink implementation. This solution is ideal if your consumer is slower, since source data is only read when the consumer is ready.

const streamParser = N3.StreamParser(),
      rdfStream = fs.createReadStream('cartoons.ttl');
rdfStream.pipe(streamParser);
streamParser.pipe(new SlowConsumer());

function SlowConsumer() {
  const writer = new require('stream').Writable({ objectMode: true });
  writer._write = (quad, encoding, done) => {
    console.log(quad);
    setTimeout(done, 1000);
  };
  return writer;
}

A dedicated prefix event signals every prefix with prefix and term arguments.

Writing

From quads to a string

N3.Writer serializes quads as an RDF document. Write quads through addQuad.

const writer = N3.Writer({ prefixes: { c: 'http://example.org/cartoons#' } });
writer.addQuad(
  namedNode('http://example.org/cartoons#Tom'),
  namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'),
  namedNode('http://example.org/cartoons#Cat')
);
writer.addQuad(quad(
  namedNode('http://example.org/cartoons#Tom'),
  namedNode('http://example.org/cartoons#name'),
  literal('Tom')
));
writer.end((error, result) => console.log(result));

By default, N3.Writer writes Turtle (or TriG if some quads are in a named graph).
To write N-Triples (or N-Quads) instead, pass a format argument upon creation:

const writer1 = N3.Writer({ format: 'N-Triples' });
const writer2 = N3.Writer({ format: 'application/trig' });

From quads to an RDF stream

N3.Writer can also write quads to a Node.js stream.

const writer = N3.Writer(process.stdout, { end: false, prefixes: { c: 'http://example.org/cartoons#' } });
writer.addQuad(
  namedNode('http://example.org/cartoons#Tom'),
  namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'),
  namedNode('http://example.org/cartoons#Cat')
);
writer.addQuad(quad(
  namedNode('http://example.org/cartoons#Tom'),
  namedNode('http://example.org/cartoons#name'),
  literal('Tom')
));
writer.end();

From a quad stream to an RDF stream

N3.StreamWriter is a Node.js stream and RDF.js Sink implementation.

const streamParser = new N3.StreamParser(),
      inputStream = fs.createReadStream('cartoons.ttl'),
      streamWriter = new N3.StreamWriter({ prefixes: { c: 'http://example.org/cartoons#' } });
inputStream.pipe(streamParser);
streamParser.pipe(streamWriter);
streamWriter.pipe(process.stdout);

Blank nodes and lists

You might want to use the […] and list (…) notations of Turtle and TriG. However, a streaming writer cannot create these automatically: the shorthand notations are only possible if blank nodes or list heads are not used later on, which can only be determined conclusively at the end of the stream.

The blank and list functions allow you to create them manually instead:

const writer = N3.Writer({ prefixes: { c: 'http://example.org/cartoons#',
                                       foaf: 'http://xmlns.com/foaf/0.1/' } });
writer.addQuad(
  writer.blank(
    namedNode('http://xmlns.com/foaf/0.1/givenName'),
    literal('Tom', 'en')),
  namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'),
  namedNode('http://example.org/cartoons#Cat')
);
writer.addQuad(quad(
  namedNode('http://example.org/cartoons#Jerry'),
  namedNode('http://xmlns.com/foaf/0.1/knows'),
  writer.blank([{
    predicate: namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'),
    object:    namedNode('http://example.org/cartoons#Cat'),
  },{
    predicate: namedNode('http://xmlns.com/foaf/0.1/givenName'),
    object:    literal('Tom', 'en'),
  }])
));
writer.addQuad(
  namedNode('http://example.org/cartoons#Mammy'),
  namedNode('http://example.org/cartoons#hasPets'),
  writer.list([
    namedNode('http://example.org/cartoons#Tom'),
    namedNode('http://example.org/cartoons#Jerry'),
  ])
);
writer.end((error, result) => console.log(result));

Storing

N3.Store allows you to store triples in memory and find them fast.

In this example, we create a new store and add the triples :Pluto a :Dog. and :Mickey a :Mouse.
Then, we find triples with :Mickey as subject.

const store = N3.Store();
store.addQuad(
  namedNode('http://ex.org/Pluto'), 
  namedNode('http://ex.org/type'),
  namedNode('http://ex.org/Dog')
);
store.addQuad(
  namedNode('http://ex.org/Mickey'),
  namedNode('http://ex.org/type'),
  namedNode('http://ex.org/Mouse')
);

const mickey = store.getQuads(namedNode('http://ex.org/Mickey'), null, null)[0];
console.log(mickey);

Addition and deletion of quads

The store provides the following manipulation methods (documentation):

  • addQuad to insert one quad
  • addQuads to insert an array of quads
  • removeQuad to remove one quad
  • removeQuads to remove an array of quads
  • createBlankNode returns an unused blank node identifier

Searching quads or entities

The store provides the following search methods (documentation):

  • getQuads returns an array of quads matching the given pattern
  • countQuads counts the number of quads matching the given pattern
  • forEach executes a callback on all matching quads
  • every returns whether a callback on matching quads always returns true
  • some returns whether a callback on matching quads returns true at least once
  • getSubjects returns an array of unique subjects occurring in matching quads
  • forSubjects executes a callback on unique subjects occurring in matching quads
  • getPredicates returns an array of unique predicates occurring in matching quad
  • forPredicates executes a callback on unique predicates occurring in matching quads
  • getObjects returns an array of unique objects occurring in matching quad
  • forObjects executes a callback on unique objects occurring in matching quads
  • getGraphs returns an array of unique graphs occurring in matching quad
  • forGraphs executes a callback on unique graphs occurring in matching quads

Compatibility

Format specifications

The N3.js parser and writer is fully compatible with the following W3C specifications:

In addition, the N3.js parser also supports Notation3 (N3) (no official specification yet).

Pass a format option to the constructor with the name or MIME type of a format for strict, fault-intolerant behavior.

Interface specifications

The N3.js submodules are compatible with the following RDF.js interfaces:

License and contributions

The N3.js library is copyrighted by Ruben Verborgh and released under the MIT License.

Contributions are welcome, and bug reports or pull requests are always helpful. If you plan to implement a larger feature, it's best to contact me first.