# The hardf turtle, n-triples, n-quads, TriG and N3 parser for PHP
[![Build Status](https://travis-ci.org/pietercolpaert/hardf.svg?branch=master)](https://travis-ci.org/pietercolpaert/hardf)

**hardf** is a PHP 7.1+ library that lets you handle Linked Data (RDF). It offers:
 - [**Parsing**](#parsing) triples/quads from [Turtle](http://www.w3.org/TR/turtle/), [TriG](http://www.w3.org/TR/trig/), [N-Triples](http://www.w3.org/TR/n-triples/), [N-Quads](http://www.w3.org/TR/n-quads/), and [Notation3 (N3)](https://www.w3.org/TeamSubmission/n3/)
 - [**Writing**](#writing) triples/quads to [Turtle](http://www.w3.org/TR/turtle/), [TriG](http://www.w3.org/TR/trig/), [N-Triples](http://www.w3.org/TR/n-triples/), and [N-Quads](http://www.w3.org/TR/n-quads/)

Both the parser as the serializer have _streaming_ support.

_This library is a port of [N3.js](https://github.com/rdfjs/N3.js/tree/v0.10.0) to PHP_

## Triple Representation

We use the triple representation in  PHP ported from NodeJS N3.js library. Check https://github.com/rdfjs/N3.js/tree/v0.10.0#triple-representation for more information

On purpose, we focused on performance, and not on developer friendliness.
We have thus implemented this triple representation using associative arrays rather than PHP object. Thus, the same that holds for N3.js, is now an array. E.g.:

```php
<?php
$triple = [
    'subject' =>   'http://example.org/cartoons#Tom',
    'predicate' => 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type',
    'object' =>    'http://example.org/cartoons#Cat',
    'graph' =>     'http://example.org/mycartoon', #optional
    ];
```

Encode literals as follows (similar to N3.js)

```php
'"Tom"@en-gb' // lowercase language
'"1"^^http://www.w3.org/2001/XMLSchema#integer' // no angular brackets <>
```

## Library functions

Install this library using [composer](http://getcomposer.org):

```bash
composer require pietercolpaert/hardf
```

### Writing
```php
use pietercolpaert\hardf\TriGWriter;
```

A class that should be instantiated and can write TriG or Turtle

Example use:
```php
$writer = new TriGWriter([
    "prefixes" => [
        "schema" =>"http://schema.org/",
        "dct" =>"http://purl.org/dc/terms/",
        "geo" =>"http://www.w3.org/2003/01/geo/wgs84_pos#",
        "rdf" => "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
        "rdfs"=> "http://www.w3.org/2000/01/rdf-schema#"
        ],
    "format" => "n-quads" //Other possible values: n-quads, trig or turtle
]);

$writer->addPrefix("ex","http://example.org/");
$writer->addTriple("schema:Person","dct:title","\"Person\"@en","http://example.org/#test");
$writer->addTriple("schema:Person","schema:label","\"Person\"@en","http://example.org/#test");
$writer->addTriple("ex:1","dct:title","\"Person1\"@en","http://example.org/#test");
$writer->addTriple("ex:1","http://www.w3.org/1999/02/22-rdf-syntax-ns#type","schema:Person","http://example.org/#test");
$writer->addTriple("ex:2","dct:title","\"Person2\"@en","http://example.org/#test");
$writer->addTriple("schema:Person","dct:title","\"Person\"@en","http://example.org/#test2");
echo $writer->end();
```

#### All methods
```php
//The method names should speak for themselves:
$writer = new TriGWriter(["prefixes": [ /* ... */]]);
$writer->addTriple($subject, $predicate, $object, $graphl);
$writer->addTriples($triples);
$writer->addPrefix($prefix, $iri);
$writer->addPrefixes($prefixes);
//Creates blank node($predicate and/or $object are optional)
$writer->blank($predicate, $object);
//Creates rdf:list with $elements
$list = $writer->addList($elements);

//Returns the current output it is already able to create and clear the internal memory use (useful for streaming)
$out .= $writer->read();
//Alternatively, you can listen for new chunks through a callback:
$writer->setReadCallback(function ($output) { echo $output });

//Call this at the end. The return value will be the full triple output, or the rest of the output such as closing dots and brackets, unless a callback was set.
$out .= $writer->end();
//OR
$writer->end();
```

### Parsing

Next to [TriG](https://www.w3.org/TR/trig/), the TriGParser class also parses [Turtle](https://www.w3.org/TR/turtle/), [N-Triples](https://www.w3.org/TR/n-triples/), [N-Quads](https://www.w3.org/TR/n-quads/) and the [W3C Team Submission N3](https://www.w3.org/TeamSubmission/n3/)

#### All methods

```php
$parser = new TriGParser($options, $tripleCallback, $prefixCallback);
$parser->setTripleCallback($function);
$parser->setPrefixCallback($function);
$parser->parse($input, $tripleCallback, $prefixCallback);
$parser->parseChunk($input);
$parser->end();
```

#### Basic examples for small files

Using return values and passing these to a writer:
```php
use pietercolpaert\hardf\TriGParser;
use pietercolpaert\hardf\TriGWriter;
$parser = new TriGParser(["format" => "n-quads"]); //also parser n-triples, n3, turtle and trig. Format is optional
$writer = new TriGWriter();
$triples = $parser->parse("<A> <B> <C> <G> .");
$writer->addTriples($triples);
echo $writer->end();
```

Using callbacks and passing these to a writer:
```php
$parser = new TriGParser();
$writer = new TriGWriter(["format"=>"trig"]);
$parser->parse("<http://A> <https://B> <http://C> <http://G> . <A2> <https://B2> <http://C2> <http://G3> .", function ($e, $triple) use ($writer) {
    if (!isset($e) && isset($triple)) {
        $writer->addTriple($triple);
        echo $writer->read(); //write out what we have so far
    } else if (!isset($triple))      // flags the end of the file
        echo $writer->end();  //write the end
    else
        echo "Error occured: " . $e;
});
```

#### Example using chunks and keeping prefixes

When you need to parse a large file, you will need to parse only chunks and already process them. You can do that as follows:

```php
$writer = new TriGWriter(["format"=>"n-quads"]);
$tripleCallback = function ($error, $triple) use ($writer) {
    if (isset($error))
        throw $error;
    else if (isset($triple)) {
        $writer->write();
        echo $writer->read();
    else if (isset($error)) {
        throw $error;
    } else {
        echo $writer->end();
    }
};
$prefixCallback = function ($prefix, $iri) use (&$writer) {
    $writer->addPrefix($prefix, $iri);
};
$parser = new TriGParser(["format" => "trig"], $tripleCallback, $prefixCallback);
$parser->parseChunk($chunk);
$parser->parseChunk($chunk);
$parser->parseChunk($chunk);
$parser->end(); //Needs to be called
```

#### Parser options

* `format` input format (case-insensitive)
  * if not provided or not matching any options below, then any [Turtle](https://www.w3.org/TR/turtle/), [TriG](https://www.w3.org/TR/trig/), [N-Triples](https://www.w3.org/TR/n-triples/) or [N-Quads](https://www.w3.org/TR/n-quads/) input can be parsed (but NOT the [N3](https://www.w3.org/TeamSubmission/n3/))
  * `turtle` - [Turtle](https://www.w3.org/TR/turtle/)
  * `trig` - [TriG](https://www.w3.org/TR/trig/)
  * contains `triple`, e.g. `triple`, `ntriples`, `N-Triples` - [N-Triples](https://www.w3.org/TR/n-triples/)
  * contains `quad`, e.g. `quad`, `nquads`, `N-Quads` - [N-Quads](https://www.w3.org/TR/n-quads/)
  * contains `n3`, e.g. `n3` - [N3](https://www.w3.org/TeamSubmission/n3/)
* `blankNodePrefix` (defaults to `b0_`) prefix forced on blank node names, e.g. `TriGWriter(["blankNodePrefix" => 'foo'])` will parse `_:bar` as `_:foobar`.
* `documentIRI` sets the base URI used to resolve relative URIs (not applicable if `format` indicates n-triples or n-quads)
* `lexer` allows usage of own lexer class. A lexer must provide following public methods:
  * `tokenize(string $input, bool $finalize = true): array<array{'subject': string, 'predicate': string, 'object': string, 'graph': string}>`
  * `tokenizeChunk(string $input): array<array{'subject': string, 'predicate': string, 'object': string, 'graph': string}>`
  * `end(): array<array{'subject': string, 'predicate': string, 'object': string, 'graph': string}>`
* `explicitQuantifiers` - [...]

### Utility
```php
use pietercolpaert\hardf\Util;
```

A static class with a couple of helpful functions for handling our specific triple representation. It will help you to create and evaluate literals, IRIs, and expand prefixes.

```php
$bool = isIRI($term);
$bool = isLiteral($term);
$bool = isBlank($term);
$bool = isDefaultGraph($term);
$bool = inDefaultGraph($triple);
$value = getLiteralValue($literal);
$literalType = getLiteralType($literal);
$lang = getLiteralLanguage($literal);
$bool = isPrefixedName($term);
$expanded = expandPrefixedName($prefixedName, $prefixes);
$iri = createIRI($iri);
$literalObject = createLiteral($value, $modifier = null);
```

See the documentation at https://github.com/RubenVerborgh/N3.js#utility for more information.

## Two executables

We also offer 2 simple tools in `bin/` as an example implementation: one validator and one translator. Try for example:
```bash
curl -H "accept: application/trig" http://fragments.dbpedia.org/2015/en | php bin/validator.php trig
curl -H "accept: application/trig" http://fragments.dbpedia.org/2015/en | php bin/convert.php trig n-triples
```

## Performance

We compared the performance on two turtle files, and parsed it with the EasyRDF library in PHP, the N3.js library for NodeJS and with Hardf. These were the results:

| #triples | framework               | time (ms) | memory (MB) |
|----------:|-------------------------|------:|--------:|
|1,866    | __Hardf__ without opcache |  27.6   |   0.722     |
|1,866    | __Hardf__ with opcache    |   24.5   |    0.380    |
|1,866    | [EasyRDF](https://github.com/njh/easyrdf) without opcache |   5,166.5   |    2.772   |
|1,866    | [EasyRDF](https://github.com/njh/easyrdf) with opcache    |  5,176.2    |  2.421     |
|1,866    | [ARC2](https://github.com/semsol/arc2) with opcache | 71.9 | 1.966 |
| 1,866  |   [N3.js](https://github.com/RubenVerborgh/N3.js) |  24.0    |  28.xxx  |
| 3,896,560  |   __Hardf__ without opcache |  40,017.7    |  0.722   |
| 3,896,560  |   __Hardf__ with opcache |    33,155.3  |    0.380   |
| 3,896,560  |   [N3.js](https://github.com/RubenVerborgh/N3.js) |  7,004.0    |  59.xxx    |
| 3,896,560  |  [ARC2](https://github.com/semsol/arc2) with opcache | 203,152.6 | 3,570.808  |

## License, status and contributions
The hardf library is copyrighted by [Ruben Verborgh](http://ruben.verborgh.org/) and [Pieter Colpaert](https://pietercolpaert.be)
and released under the [MIT License](https://github.com/pietercolpaert/hardf/blob/master/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 discuss this first by filing an issue.