php-json-ld

Introduction

This library is an implementation of the JSON-LD specification in PHP.

JSON, as specified in RFC7159, is a simple language for representing objects on the Web. Linked Data is a way of describing content across different documents or Web sites. Web resources are described using IRIs, and typically are dereferencable entities that may be used to find more information, creating a "Web of Knowledge". JSON-LD is intended to be a simple publishing method for expressing not only Linked Data in JSON, but for adding semantics to existing JSON.

JSON-LD is designed as a light-weight syntax that can be used to express Linked Data. It is primarily intended to be a way to express Linked Data in JavaScript and other Web-based programming environments. It is also useful when building interoperable Web Services and when storing Linked Data in JSON-based document storage engines. It is practical and designed to be as simple as possible, utilizing the large number of JSON parsers and existing code that is in use today. It is designed to be able to express key-value pairs, RDF data, RDFa data, Microformats data, and Microdata. That is, it supports every major Web-based structured data model in use today.

The syntax does not require many applications to change their JSON, but easily add meaning by adding context in a way that is either in-band or out-of-band. The syntax is designed to not disturb already deployed systems running on JSON, but provide a smooth migration path from JSON to JSON with added semantics. Finally, the format is intended to be fast to parse, fast to generate, stream-based and document-based processing compatible, and require a very small memory footprint in order to operate.

Quick Examples

$doc = (object)array(
  "http://schema.org/name" => "Manu Sporny",
  "http://schema.org/url" => (object)array("@id" => "http://manu.sporny.org/"),
  "http://schema.org/image" => (object)array("@id" => "http://manu.sporny.org/images/manu.png")
);

$context = (object)array(
  "name" => "http://schema.org/name",
  "homepage" => (object)array("@id" => "http://schema.org/url", "@type" => "@id"),
  "image" => (object)array("@id" => "http://schema.org/image", "@type" => "@id")
);

// compact a document according to a particular context
// see: http://json-ld.org/spec/latest/json-ld/#compacted-document-form
$compacted = jsonld_compact($doc, $context);

echo json_encode($compacted, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
/* Output:
{
  "@context": {...},
  "image": "http://manu.sporny.org/images/manu.png",
  "homepage": "http://manu.sporny.org/",
  "name": "Manu Sporny"
}
*/

// compact using URLs
jsonld_compact('http://example.org/doc', 'http://example.org/context');

// expand a document, removing its context
// see: http://json-ld.org/spec/latest/json-ld/#expanded-document-form
$expanded = jsonld_expand($compacted) {
echo json_encode($expanded, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
/* Output:
{
  "http://schema.org/image": [{"@id": "http://manu.sporny.org/images/manu.png"}],
  "http://schema.org/name": [{"@value": "Manu Sporny"}],
  "http://schema.org/url": [{"@id": "http://manu.sporny.org/"}]
}
*/

// expand using URLs
jsonld_expand('http://example.org/doc');

// flatten a document
// see: http://json-ld.org/spec/latest/json-ld/#flattened-document-form
$flattened = jsonld_flatten($doc);
// all deep-level trees flattened to the top-level

// frame a document
// see: http://json-ld.org/spec/latest/json-ld-framing/#introduction
$framed = jsonld_frame($doc, $frame);
// document transformed into a particular tree structure per the given frame

// normalize a document using the RDF Dataset Normalization Algorithm
// (URDNA2015), see: http://json-ld.github.io/normalization/spec/
$normalized = jsonld_normalize(
  $doc, array('algorithm' => 'URDNA2015', 'format' => 'application/nquads'));
// normalized is a string that is a canonical representation of the document
// that can be used for hashing, comparison, etc.

// force HTTPS-only context loading:
// use built-in secure document loader
jsonld_set_document_loader('jsonld_default_secure_document_loader');

// set a default custom document loader
jsonld_set_document_loader('my_custom_doc_loader');

// a custom loader that demonstrates using a simple in-memory mock for
// certain contexts before falling back to the default loader
// note: if you want to set this loader as the new default, you'll need to
// store the previous default in another variable first and access that inside
// the loader
global $mocks;
$mocks = array('http://example.com/mycontext' => (object)array(
  'hombre' => 'http://schema.org/name'));
function mock_load($url) {
  global $jsonld_default_load_document, $mocks;
  if(isset($mocks[$url])) {
    // return a "RemoteDocument", it has these three properties:
    return (object)array(
      'contextUrl' => null,
      'document' => $mocks[$url],
      'documentUrl' => $url);
  }
  // use default loader
  return call_user_func($jsonld_default_load_document, $url);
}

// use the mock loader for just this call, witout modifying the default one
$compacted = jsonld_compact($foo, 'http://example.com/mycontext', array(
  'documentLoader' => 'mock_load'));

// a custom loader that uses a simplistic in-memory cache (no invalidation)
global $cache;
$cache = array();
function cache_load($url) {
  global $jsonld_default_load_document, $cache;
  if(isset($cache[$url])) {
    return $cache[$url];
  }
  // use default loader
  $doc = call_user_func($jsonld_default_load_document, $url);
  $cache[$url] = $doc;
  return $doc;
}

// use the cache loader for just this call, witout modifying the default one
$compacted = jsonld_compact($foo, 'http://schema.org', array(
  'documentLoader' => 'cache_load'));

Source

The source code for the PHP implementation of the JSON-LD API is available at:

https://git.friendi.ca/friendica/php-json-ld

Tests

This library includes a sample testing utility which may be used to verify that changes to the processor maintain the correct output.

To run the sample tests you will need to get the test suite files by cloning the json-ld.org and normalization repositories hosted on GitHub:

• https://github.com/json-ld/json-ld.org
• https://github.com/json-ld/normalization

Then run the PHPUnit test.php application and point it at the directories containing the tests:

phpunit --group json-ld.org test.php -d {PATH_TO_JSON_LD_ORG/test-suite}
phpunit --group normalization test.php -d {PATH_TO_NORMALIZATION/tests}