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<!DOCTYPE html>
<html lang="en">
<head>
<title>JSON-LD 1.1 Processing Algorithms and API</title>
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</head>
<body>
<section id="abstract">
<p>This specification defines a set of algorithms for programmatic transformations
of JSON-LD documents. Restructuring data according to the defined transformations
often dramatically simplifies its usage. Furthermore, this document proposes
an Application Programming Interface (API) for developers implementing the
specified algorithms.</p>
</section>
<section id="sotd">
<p>This document has been developed by the
<a href="https://www.w3.org/2018/json-ld-wg/">JSON-LD Working Group</a> and was derived from the <a href="https://www.w3.org/community/json-ld/">JSON-LD Community Group's</a> <a href="https://www.w3.org/2018/jsonld-cg-reports/json-ld-api/">Final Report</a>.</p>
<p>There is a
<a href="https://json-ld.org/playground/">live JSON-LD playground</a> that is capable
of demonstrating the features described in this document.</p>
<section>
<h2>Set of Documents</h2>
<p>This document is one of three JSON-LD 1.1 Recommendations produced by the
<a href="https://www.w3.org/2018/json-ld-wg/">JSON-LD Working Group</a>:</p>
<ul>
<li>[[[JSON-LD11]]]</li>
<li><a href="">JSON-LD 1.1 Processing Algorithms and API</a></li>
<li>[[[JSON-LD11-FRAMING]]]</li>
</ul>
</section>
</section>
<section class="informative">
<h1>Introduction</h1>
<p>This document is a detailed specification of the JSON-LD processing algorithms.
The document is primarily intended for the following audiences:</p>
<ul>
<li>Software developers who want to implement the algorithms to transform
JSON-LD documents.</li>
<li>Web authors and developers who want a very detailed view of how
a <a>JSON-LD Processor</a> operates.</li>
<li>Developers who want an overview of the proposed JSON-LD API.</li>
</ul>
<p>To understand the basics in this specification you must first be familiar with
<a data-cite="RFC8259" data-no-xref="">JSON</a>, which is detailed in [[RFC8259]]. You must also understand the
JSON-LD syntax defined in the <a data-cite="JSON-LD11" data-no-xref="">JSON-LD 1.1 Syntax specification</a> [[JSON-LD11]], which is the base syntax used by all
of the algorithms in this document. To understand the API and how it is
intended to operate in a programming environment, it is useful to have working
knowledge of the JavaScript programming language [[ECMASCRIPT]] and
WebIDL [[WEBIDL]]. To understand how JSON-LD maps to RDF, it is helpful to be
familiar with the basic RDF concepts [[RDF11-CONCEPTS]].</p>
<section class="informative">
<h2>Contributing</h2>
<p>There are a number of ways that one may participate in the development of
this specification:</p>
<ul>
<li>Technical discussion typically occurs on the public mailing list:
<a href="https://lists.w3.org/Archives/Public/public-json-ld-wg/">public-json-ld-wg@w3.org</a></li>
<!--<li><a href="https://json-ld.org/minutes/">Public teleconferences</a> are held
on Tuesdays at 1500UTC on the second and fourth week of each month.</li> -->
<li>The #json-ld
IRC channel is available for real-time discussion on <a href="http://irc.w3.org">irc.w3c.org</a>.</li>
</ul>
</section>
<section class="informative">
<h2>Typographical conventions</h2>
<div data-include="common/typographical-conventions.html"></div>
<section>
<h3>Summarized algorithm sections</h3>
<p>In order to make the algorithms easier to read,
some parts of them are initially hidden and replaced by a short summary.
Clicking on that summary will toggle between detailed and summarised view.
Using the buttons below, you can display or hide the details in all algorithms at once.
Note that, when printing, all details are always shown.
</p>
<p>
<button id="unfold-all-algorithms">Show all details in all algorithms</button>
<button id="fold-all-algorithms">Hide all details in all algorithms</button>
</p>
</section>
</section>
<section class="normative">
<h2>Terminology</h2>
<p>This document uses the following terms as defined in external specifications
and defines terms specific to JSON-LD.</p>
<div data-include="common/terms.html"
data-oninclude="restrictReferences">
</div>
<section>
<h4>Algorithm Terms</h4>
<p>The Following terms are used within specific algorithms.</p>
<div data-include="common/algorithm-terms.html"
data-oninclude="restrictReferences">
</div>
</section>
</section>
<section class="informative">
<h3>Example Conventions</h3>
<p>Note that in the examples used in this document, output
is of necessity shown in serialized form as JSON. While the algorithms
describe operations on the <a>JSON-LD internal representation</a>, when
they as displayed as examples, the JSON serialization is used. In particular,
the internal representation use of <a>maps</a> are represented using
<a>JSON objects</a>.</p>
<pre class="example nohighlight input" data-transform="updateExample"
title="Sample JSON-LD document">
<!--
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"knows": "http://xmlns.com/foaf/0.1/knows"
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"@id": "http://me.markus-lanthaler.com/",
"name": "Markus Lanthaler",
"knows": [
{
"name": "Dave Longley"
}
]
}
-->
</pre>
<p>In the <a>internal representation</a>, the example above would be of a
<a>map</a> containing <code>@context</code>, <code>@id</code>, <code>name</code>, and <code>knows</code> <a>entries</a>,
with either <a>maps</a>, <a>strings</a>, or <a>arrays</a> of
maps or strings values. In the JSON serialization, <a>JSON objects</a> are used
for maps, while arrays and strings are serialized using a
convention common to many programming languages.</p>
</section>
</section> <!-- end of Introduction -->
<section class="informative">
<h1>Features</h1>
<p>The JSON-LD 1.1 Syntax specification [[JSON-LD11]] defines a syntax to
express Linked Data in JSON. Because there is more than one way to
express Linked Data using this syntax, it is often useful to be able to
transform JSON-LD documents so that they may be more easily consumed by
specific applications.</p>
<p class="changed">To allow these algorithms to be adapted for syntaxes
other than JSON, the algorithms operate on the <a>JSON-LD internal representation</a>,
which uses the generic
concepts of <a>arrays</a>, <a>maps</a>,
<a>strings</a>, <a>numbers</a>, <a>booleans</a>, and <a>null</a> to describe
the data represented by a JSON document. Algorithms act on this
<a>internal representation</a> with API entry points responsible for
transforming between the concrete and internal representations.</p>
<p>JSON-LD uses <a>contexts</a> to allow Linked Data
to be expressed in a way that is specifically tailored to a particular
person or application. By providing a <a>context</a>,
JSON data can be expressed in a way that is a natural fit for a particular
person or application whilst also indicating how the data should be
understood at a global scale. In order for people or applications to
share data that was created using a <a>context</a> that is different
from their own, a JSON-LD processor must be able to transform a document
from one <a>context</a> to another. Instead of requiring JSON-LD
processors to write specific code for every imaginable
<a>context</a> switching scenario, it is much easier to specify a
single algorithm that can remove any <a>context</a>. Similarly,
another algorithm can be specified to subsequently apply any
<a>context</a>. These two algorithms represent the most basic
transformations of JSON-LD documents. They are referred to as
<a>expansion</a> and <a>compaction</a>, respectively.</p>
<p class="changed">JSON-LD 1.1 introduces new features that are
compatible with [[[JSON-LD]]] [[JSON-LD]],
but if processed by a JSON-LD 1.0 processor may produce different results.
In order to detect this JSON-LD 1.1 requires that the <a>processing
mode</a> be explicitly set to <code>json-ld-1.1</code>, either through the
<a data-link-for="JsonLdOptions">processingMode</a> API option, or using the
<code>@version</code> <a>map entry</a> within a <a>context</a>.</p>
<p>There are four major types of transformation that are discussed in this
document: expansion, compaction, flattening, and RDF serialization/deserialization.</p>
<section class="informative">
<h2>Expansion</h2>
<p>The algorithm that removes <a>context</a> is
called <dfn data-lt="expanded|expanding">expansion</dfn>. Before performing any other
transformations on a JSON-LD document, it is easiest to
remove any <a>context</a> from it and to make data structures
more regular.</p>
<p>To get an idea of how context and data structuring affects the same data,
here is an example of JSON-LD that uses only <a>terms</a>
and is fairly compact:</p>
<aside class="example ds-selector-tabs"
title="JSON-LD document using only terms">
<div class="selectors">
<button class="selected input" data-selects="compacted">Compacted (Input)</button>
<button data-selects="expanded">Expanded (Result)</button>
<button data-selects="statements">Statements</button>
<button data-selects="turtle">Turtle</button>
<a class="playground" target="_blank"></a>
</div>
<pre class="compacted selected" data-transform="updateExample">
<!--
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"homepage": {
"@id": "http://xmlns.com/foaf/0.1/homepage",
"@type": "@id"
}
},
"@id": "http://me.markus-lanthaler.com/",
"name": "Markus Lanthaler",
"homepage": "http://www.markus-lanthaler.com/"
}
-->
</pre>
<pre class="expanded result"
data-result-for="JSON-LD document using only terms-compacted"
data-transform="updateExample">
<!--
[{
"@id": "http://me.markus-lanthaler.com/",
"http://xmlns.com/foaf/0.1/name": [
{"@value": "Markus Lanthaler"}
],
"http://xmlns.com/foaf/0.1/homepage": [
{"@id": "http://www.markus-lanthaler.com/"}
]
}]
-->
</pre>
<table class="statements"
data-result-for="JSON-LD document using only terms-expanded">
<thead><tr><th>Subject</th><th>Property</th><th>Value</th></tr></thead>
<tbody>
<tr><td>http://me.markus-lanthaler.com/</td><td>foaf:name</td><td>Markus Lanthaler</td></tr>
<tr><td>http://me.markus-lanthaler.com/</td><td>http://xmlns.com/foaf/0.1/homepage</td><td>http://www.markus-lanthaler.com/</td></tr>
</tbody>
</table>
<pre class="turtle"
data-content-type="text/turtle"
data-result-for="JSON-LD document using only terms-expanded"
data-transform="updateExample"
data-to-rdf>
<!--
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
<http://me.markus-lanthaler.com/> foaf:name "Markus Lanthaler";
foaf:homepage <http://www.markus-lanthaler.com/> .
-->
</pre>
</aside>
<p>The next input example uses one <a>IRI</a> to express a <a>property</a>
and an <a>array</a> to encapsulate another, but
leaves the rest of the information untouched.</p>
<aside class="example ds-selector-tabs"
title="Sample JSON-LD document using an IRI instead of a term to express a property">
<div class="selectors">
<a class="playground" target="_blank"></a>
</div>
<pre class="compacted input selected nohighlight" data-transform="updateExample">
<!--
{
"@context": {
****"website": "http://xmlns.com/foaf/0.1/homepage"****
},
"@id": "http://me.markus-lanthaler.com/",
"****http://xmlns.com/foaf/0.1/name****": "Markus Lanthaler",
****"website"****: ****{ "@id":**** "http://www.markus-lanthaler.com/" ****}****
}
-->
</pre>
</aside>
<p>Note that both inputs are valid JSON-LD and both represent the same
information. The difference is in their <a>context</a> information
and in the data structures used. A JSON-LD processor can remove
<a>context</a> and ensure that the data is more regular by employing
<a>expansion</a>.</p>
<p><a>Expansion</a> has two important goals: removing any contextual
information from the document, and ensuring all values are represented
in a regular form. These goals are accomplished by expanding all <a>entry</a> keys
to <a>absolute IRIs</a> and by expressing all
values in <a>arrays</a> in
<a>expanded form</a>. <a>Expanded form</a> is the most verbose
and regular way of expressing of values in JSON-LD; all contextual
information from the document is instead stored locally with each value.
Running the <a href="#expansion-algorithm">Expansion algorithm</a>
(<a data-link-for="JsonLdProcessor">expand()</a>)
operation) against the above examples results in the following output:</p>
<pre class="example result nohighlight" data-transform="updateExample"
data-result-for="Sample JSON-LD document using an IRI instead of a term to express a property-compacted"
title="Expanded JSON-LD document using an IRI">
<!--
[
{
"@id": "http://me.markus-lanthaler.com/",
"****http://xmlns.com/foaf/0.1/name****": [
{ "@value": "Markus Lanthaler" }
],
"****http://xmlns.com/foaf/0.1/homepage****": [
{ "@id": "http://www.markus-lanthaler.com/" }
]
}
]
-->
</pre>
<p class="changed">The example above is the JSON-LD serialization of the output of the
<a href="#expansion-algorithm">expansion algorithm</a>,
where the algorithm's use of <a>maps</a> are replaced with <a>JSON objects</a>.</p>
<p>Note that in the output above all <a>context</a> definitions have
been removed, all <a>terms</a> and
<a>compact IRIs</a> have been expanded to absolute
<a>IRIs</a>, and all
<a>JSON-LD values</a> are expressed in
<a>arrays</a> in <a>expanded form</a>. While the
output is more verbose and difficult for a human to read, it establishes a
baseline that makes JSON-LD processing easier because of its very regular
structure.</p>
</section> <!-- end of Expansion -->
<section class="informative">
<h2>Compaction</h2>
<p>While <a>expansion</a> removes <a>context</a> from a given
input, <dfn data-lt="compact|compacting|compacted|compacts">compaction</dfn>'s primary function is to
perform the opposite operation: to express a given input according to
a particular <a>context</a>. <a>Compaction</a> applies a
<a>context</a> that specifically tailors the way information is
expressed for a particular person or application. This simplifies applications
that consume JSON or JSON-LD by expressing the data in application-specific
terms, and it makes the data easier to read by humans.</p>
<p><a>Compaction</a> uses a developer-supplied <a>context</a> to
shorten <a>IRIs</a> to <a>terms</a> or
<a>compact IRIs</a> and
<a>JSON-LD values</a> expressed in
<a>expanded form</a> to simple values such as <a>strings</a>
or <a>numbers</a>.</p>
<p>For example, assume the following expanded JSON-LD input document:</p>
<pre id="sample-document"
class="example expanded input nohighlight" data-transform="updateExample"
title="Expanded sample document">
<!--
[
{
"@id": "http://me.markus-lanthaler.com/",
"http://xmlns.com/foaf/0.1/name": [
{ "@value": "Markus Lanthaler" }
],
"http://xmlns.com/foaf/0.1/homepage": [
{ "@id": "http://www.markus-lanthaler.com/" }
]
}
]
-->
</pre>
<p>Additionally, assume the following developer-supplied JSON-LD
<a>context</a>:</p>
<pre id="sample-document-context"
class="example context nohighlight"
data-transform="updateExample"
data-context-for="Expanded sample document"
title="JSON-LD context">
<!--
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"homepage": {
"@id": "http://xmlns.com/foaf/0.1/homepage",
"@type": "@id"
}
}
}
-->
</pre>
<p>Running the <a href="#compaction-algorithm">Compaction Algorithm</a>
(<a data-link-for="JsonLdProcessor">compact()</a>)
operation) given the context supplied above against the JSON-LD input
document provided above would result in the following output:</p>
<aside class="example ds-selector-tabs"
title="Compacted sample document">
<div class="selectors">
<a class="playground"
data-result-for="#sample-document"
data-context="#sample-document-context"
data-compact
target="_blank"></a>
</div>
<pre class="result compacted selected nohighlight" data-transform="updateExample"
data-result-for="Expanded sample document"
data-context="JSON-LD context"
data-compact
title="Compacted sample document">
<!--
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"homepage": {
"@id": "http://xmlns.com/foaf/0.1/homepage",
"@type": "@id"
}
},
"@id": "http://me.markus-lanthaler.com/",
"name": "Markus Lanthaler",
"homepage": "http://www.markus-lanthaler.com/"
}
-->
</pre>
</aside>
<p class="changed">The example above is the JSON-LD serialization of the output of the
<a href="#compaction-algorithm">compaction algorithm</a>,
where the algorithm's use of <a>maps</a> are replaced with <a>JSON objects</a>.</p>
<p>Note that all <a>IRIs</a> have been compacted to
<a>terms</a> as specified in the <a>context</a>,
which has been injected into the output. While compacted output is
useful to humans, it is also used to generate structures that are easy to
program against. Compaction enables developers to map any expanded document
into an application-specific compacted document. While the context provided
above mapped <code>http://xmlns.com/foaf/0.1/name</code> to <code>name</code>, it
could also have been mapped to any other term provided by the developer.</p>
</section> <!-- end of Compaction -->
<section class="informative">
<h2>Flattening</h2>
<p>While expansion ensures that a document is in a uniform structure,
<dfn data-lt="flattened">flattening</dfn> goes a step further to ensure that the shape of the data
is deterministic. In expanded documents, the <a>properties</a> of a single
<a>node</a> may be spread across a number of different
<a class="changed">maps</a>. By flattening a
document, all <a>properties</a> of a <a>node</a> are collected in a single
<a class="changed">map</a> and all <a>blank nodes</a>
are labeled with a <a>blank node identifier</a>. This may drastically
simplify the code required to process JSON-LD data in certain applications.</p>
<p>For example, assume the following JSON-LD input document:</p>
<pre id="json-ld-document-in-compact-form"
class="example compacted input nohighlight" data-transform="updateExample"
title="JSON-LD document in compact form">
<!--
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"knows": "http://xmlns.com/foaf/0.1/knows"
},
"@id": "http://me.markus-lanthaler.com/",
"name": "Markus Lanthaler",
"knows": [
{"name": "Dave Longley"}
]
}
-->
</pre>
<p>Running the <a href="#flattening-algorithm">Flattening Algorithm</a>
(<a data-link-for="JsonLdProcessor">flatten()</a>)
operation) with a context set to <a>null</a> to prevent compaction
returns the following document:</p>
<aside class="example ds-selector-tabs"
title="Flattened sample document">
<div class="selectors">
<a class="playground"
data-result-for="#json-ld-document-in-compact-form"
data-flatten
target="_blank"></a>
</div>
<pre class="original result selected nohighlight" data-transform="updateExample"
data-result-for="JSON-LD document in compact form"
data-flatten>
<!--
[{
"@id": "http://me.markus-lanthaler.com/",
"http://xmlns.com/foaf/0.1/name": [
{ "@value": "Markus Lanthaler" }
],
"http://xmlns.com/foaf/0.1/knows": [
{ "@id": "_:b0" }
]
}, {
"@id": "_:b0",
"http://xmlns.com/foaf/0.1/name": [
{ "@value": "Dave Longley" }
]
}]
-->
</pre>
</aside>
<p class="changed">The example above is the JSON-LD serialization of the output of the
<a href="#flattening-algorithm">flattening algorithm</a>,
where the algorithm's use of <a>maps</a> are replaced with <a>JSON objects</a>.</p>
<p>Note how in the output above all <a>properties</a> of a <a>node</a> are collected in a
single <a class="changed">map</a> and how the <a>blank node</a> representing
"Dave Longley" has been assigned the <a>blank node identifier</a>
<code>_:b0</code>.</p>
<p>To make it easier for humans to read or for certain applications to
process it, a flattened document can be compacted by passing a context. Using
the same context as the input document, the flattened and compacted document
looks as follows:</p>
<aside class="example ds-selector-tabs"
title="Flattened and compacted sample document">
<div class="selectors">
<a class="playground"
data-result-for="#json-ld-document-in-compact-form"
data-context="#json-ld-document-in-compact-form"
data-flatten
target="_blank"></a>
</div>
<pre class="result selected nohighlight" data-transform="updateExample"
data-result-for="JSON-LD document in compact form"
data-context="JSON-LD document in compact form"
data-flatten
title="Flattened and compacted sample document">
<!--
{
"@context": {
"name": "http://xmlns.com/foaf/0.1/name",
"knows": "http://xmlns.com/foaf/0.1/knows"
},
"@graph": [{
"@id": "http://me.markus-lanthaler.com/",
"name": "Markus Lanthaler",
"knows": { "@id": "_:b0" }
}, {
"@id": "_:b0",
"name": "Dave Longley"
}]
}
-->
</pre>
</aside>
<p>Please note that the result of flattening and <a>compacting</a> a document
is always a <a class="changed">map</a>,
<span class="changed">(represented as a <a>JSON object</a> when serialized)</span>,
which contains an <code>@graph</code>
<a>entry</a> that represents the <a>default graph</a>.</p>
</section> <!-- end of Flattening -->
<section class="informative">
<h2>RDF Serialization/Deserialization</h2>
<p>JSON-LD can be used to serialize RDF data as described in
[[RDF11-CONCEPTS]]. This ensures that data can be round-tripped to and from
any RDF syntax without any loss in fidelity.</p>
<p>For example, assume the following RDF input serialized in Turtle [[TURTLE]]:</p>
<pre class="example nohighlight" data-transform="updateExample"
data-content-type="text/turtle"
data-from-rdf
title="Sample Turtle document">
<!--
<http://me.markus-lanthaler.com/> <http://xmlns.com/foaf/0.1/name> "Markus Lanthaler" .
<http://me.markus-lanthaler.com/> <http://xmlns.com/foaf/0.1/homepage> <http://www.markus-lanthaler.com/> .
-->
</pre>
<p>Using the <a href="#serialize-rdf-as-json-ld-algorithm">Serialize RDF as JSON-LD Algorithm</a>
a developer could transform this document into expanded JSON-LD:</p>
<pre class="example nohighlight" data-transform="updateExample"
data-result-for="Sample Turtle document"
data-from-rdf
title="Sample Turtle document converted to JSON-LD">
<!--
[
{
"@id": "http://me.markus-lanthaler.com/",
"http://xmlns.com/foaf/0.1/name": [
{ "@value": "Markus Lanthaler" }
],
"http://xmlns.com/foaf/0.1/homepage": [
{ "@id": "http://www.markus-lanthaler.com/" }
]
}
]
-->
</pre>
<p class="changed">The example above is the JSON-LD serialization of the output of the
<a href="#serialize-rdf-as-json-ld-algorithm">Serialize RDF as JSON-LD Algorithm</a>,
where the algorithm's use of <a>maps</a> are replaced with <a>JSON objects</a>.</p>
<p>Note that the output above could easily be compacted using the technique outlined
in the previous section. It is also possible to deserialize the JSON-LD document back
to RDF using the <a href="#deserialize-json-ld-to-rdf-algorithm">Deserialize JSON-LD to RDF Algorithm</a>.</p>
</section> <!-- end of RDF Serialization/Deserialization -->
</section> <!-- end of Features section -->
<section id="conformance">
<p>There are two classes of products that can claim conformance to this
specification: <a>JSON-LD Processors</a>,
and <a>RDF Serializers/Deserializers</a>.</p>
<p>A conforming <a>JSON-LD Processor</a> is a system which can perform the
<a href="#expansion-algorithm">Expansion</a>, <a href="#compaction-algorithm">Compaction</a>,
and <a href="#flattening-algorithm">Flattening</a> operations
<span class="changed">in a manner consistent with
the algorithms defined in this specification</span>.</p>
<p><a>JSON-LD Processors</a> MUST NOT
attempt to correct malformed <a>IRIs</a> or language tags;
however, they MAY issue validation warnings. IRIs are not modified other
than conversion between <a data-lt="relative IRI">relative</a> and
<a>absolute IRIs</a>.</p>
<p>A conforming <dfn data-lt="RDF Serializers/Deserializers">RDF Serializer/Deserializer</dfn> is a system that can
<a href="#deserialize-json-ld-to-rdf-algorithm">deserialize JSON-LD to RDF</a> and
<a href="#serialize-rdf-as-json-ld-algorithm">serialize RDF as JSON-LD</a> as
defined in this specification.</p>
<p>The algorithms in this specification are generally written with more concern for clarity
than efficiency. Thus, <a>JSON-LD Processors</a> may
implement the algorithms given in this specification in any way desired,
so long as the end result is indistinguishable from the result that would
be obtained by the specification's algorithms.</p>