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Lightning fast, asynchronous, streaming Turtle for JavaScript

README.md

Lightning fast, asynchronous, streaming Turtle for JavaScript

The N3.js library lets you handle Turtle and RDF in JavaScript (Node and browser) easily. It offers:

It has the following characteristics:

  • extreme performance – by far the fastest parser in JavaScript
  • asynchronous – triples arrive as soon as possible
  • streaming – streams are parsed as data comes in, so you can easily parse files that don't fit into memory

At a later stage, this library will support Notation3 (N3), a Turtle superset.

Installation

N3.js comes as an npm package.

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

It is also fully compatible with browserify.
Alternatively, it offers a minimal browser version (without Node stream support).

$ cd n3
$ npm install
$ make browser
<script src="n3-browser.min.js"></script>

Triple representation

For maximum performance and easy of use, triples are represented as simple objects.
Since URIs are most common when dealing with RDF, they are represented as simple strings.

@prefix c: <http://example.org/cartoons#>.
c:Tom a c:Cat.

is represented as

{
  subject:   'http://example.org/cartoons#Tom',
  predicate: 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
  object:    'http://example.org/cartoons#Cat'
}

Literals are represented as double quoted strings.

c:Tom c:name "Tom".

is represented as

{
  subject:   'http://example.org/cartoons#Tom',
  predicate: 'http://example.org/cartoons#name',
  object:    '"Tom"'
}

This allows you to create and compare literals fast and easily:

triple.object === 'http://example.org/cartoons#Cat'
triple.object === '"Tom"'

The Utility section details entity representation in more depth.

Parsing

From a Turtle string to triples

N3.Parser parses strings into triples using a callback.
The callback's first argument is an error value, the second is a triple. If there are no more triples, the callback is invoked one last time with null as triple value and a hash of prefixes as the third argument.

var parser = N3.Parser();
parser.parse('@prefix c: <http://example.org/cartoons#>.\n' +
             'c:Tom a c:Cat.\n' +
             'c:Jerry a c:Mouse;\n' +
             '        c:smarterThan c:Tom.',
             function (error, triple, prefixes) {
               if (triple)
                 console.log(triple.subject, triple.predicate, triple.object, '.');
               else
                 console.log("# That's all, folks!", prefixes)
             });

Addionally, a second callback function (prefix, uri) can be passed to parse.

From Turtle fragments to triples

N3.Parser can also parse triples from a Turtle document that arrives in fragments.

var parser = N3.Parser(), triples = [];
parser.parse(function (error, triple, prefixes) { triple && triples.push(triple); });

parser.addChunk('@prefix c: <http://example.org/cartoons#>.\n');
parser.addChunk('c:Tom a ');
parser.addChunk('c:Cat. c:Jerry a');
console.log(triples); // First triple

parser.addChunk(' c:Mouse.');
parser.end();
console.log(triples); // Both triples

From a Turtle stream to triples

N3.Parser can parse streams as they grow, returning triples as soon as they're ready.
This behavior sets N3.js apart from most other Turtle libraries.

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

In addition, N3.StreamParser offers a Node Stream implementation, so you can transform Turtle streams and pipe them to anywhere. This solution is ideal if your consumer is slower, as it avoids parser backpressure.

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

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

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

Storing

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

var store = N3.Store();
store.addTriple(':Pluto', 'a', ':Dog');
store.addTriple(':Mickey', 'a', ':Mouse');

var mickey = store.find(':Mickey', null, null)[0];
console.log(mickey.subject, mickey.predicate, mickey.object, '.');

Writing

From triples to a string

N3.Writer can serialize triples as a Turtle string.

var writer = N3.Writer({ 'c': 'http://example.org/cartoons#' });
writer.addTriple('http://example.org/cartoons#Tom',
                 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
                 'http://example.org/cartoons#Cat');
writer.addTriple({
  subject:   'http://example.org/cartoons#Tom',
  predicate: 'http://example.org/cartoons#name',
  object:    '"Tom"'
});
writer.end(function (error, result) { console.log(result); });

From triples to a Turtle stream

N3.Writer can also write triples to an output stream.

var writer = N3.Writer(process.stdout, { 'c': 'http://example.org/cartoons#' });
writer.addTriple('http://example.org/cartoons#Tom',
                 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
                 'http://example.org/cartoons#Cat');
writer.addTriple({
  subject:   'http://example.org/cartoons#Tom',
  predicate: 'http://example.org/cartoons#name',
  object:    '"Tom"'
});
writer.end();

From a triple stream to a Turtle stream

N3.StreamWriter is a Turtle writer implementation as a Node Stream.

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

Utility

N3.Util offers helpers for URI and literal representations.
As URIs are most common, they are represented as simple strings:

var N3Util = N3.Util;
N3Util.isUri('http://example.org/cartoons#Mickey'); // true

Literals are represented as double quoted strings:

N3Util.isLiteral('"Mickey Mouse"'); // true
N3Util.getLiteralValue('"Mickey Mouse"'); // 'Mickey Mouse'
N3Util.isLiteral('"Mickey Mouse"@en'); // true
N3Util.getLiteralLanguage('"Mickey Mouse"@en'); // 'en'
N3Util.isLiteral('"3"^^<http://www.w3.org/2001/XMLSchema#integer>'); // true
N3Util.getLiteralType('"3"^^<http://www.w3.org/2001/XMLSchema#integer>'); // 'http://www.w3.org/2001/XMLSchema#integer'
N3Util.isLiteral('"http://example.org/"'); // true
N3Util.getLiteralValue('"http://example.org/"'); // 'http://example.org/'

Note the difference between 'http://example.org/' (URI) and '"http://example.org/"' (literal).
Also note that the double quoted literals are not raw Turtle syntax:

N3Util.isLiteral('"This word is "quoted"!"'); // true

The above string represents the string This word is "quoted"!, even though the correct Turtle syntax for that is "This word is \"quoted\"!" N3.js thus always parses literals, but adds quotes to differentiate from URIs:

new N3.Parser().parse('<a> <b> "This word is \\"quoted\\"!".', console.log);
// { subject: 'a', predicate: 'b', object: '"This word is "quoted"!"' }

Blank nodes start with _:, and can be tested for as follows:

N3Util.isBlank('_:b1'); // true
N3Util.isUri('_:b1'); // false
N3Util.isLiteral('_:b1'); // false

QNames can be tested and expanded:

var prefixes = { 'rdfs': 'http://www.w3.org/2000/01/rdf-schema#' };
N3Util.isQName('rdfs:label'); // true;
N3Util.expandQName('rdfs:label', prefixes); // http://www.w3.org/2000/01/rdf-schema#label

Loading the utility globally

For convenience, N3Util can also be loaded globally:

require('n3').Util(global);
isUri('http://example.org/cartoons#Mickey'); // true
isLiteral('"Mickey Mouse"'); // true

If desired, the methods can even be added directly on all strings:

require('n3').Util(String, true);
'http://example.org/cartoons#Mickey'.isUri(); // true
'"Mickey Mouse"'.isLiteral(); // true

License, status and contributions

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

Build Status
Browser Build Status

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

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