This document is also available in this non-normative format: diff to previous version
Copyright © 2010-2013 W3C ® ( MIT , ERCIM , Keio , Beihang ), All Rights Reserved. W3C liability , trademark and document use rules apply.
JSON is a useful data serialization and messaging format. This specification defines JSON-LD, a JSON-based format to serialize Linked Data. The syntax is designed to easily integrate into deployed systems that already use JSON, and provides a smooth upgrade path from JSON to JSON-LD. It is primarily intended to be a way to use Linked Data in Web-based programming environments, to build interoperable Web services, and to store Linked Data in JSON-based storage engines.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This
document
has
been
under
development
for
over
30
31
months
in
the
JSON
for
Linking
Data
Community
Group.
The
document
has
been
transferred
to
the
RDF
Working
Group
for
review,
improvement,
and
publication.
The
specification
has
undergone
significant
development,
review,
and
changes
during
the
course
of
the
last
30
31
months.
There
are
several
independent
interoperable
implementations
of
this
specification.
There
is
a
fairly
complete
test
suite
[
JSON-LD-TESTS
]
and
a
live
JSON-LD
editor
that
is
capable
of
demonstrating
the
features
described
in
this
document.
While
development
on
implementations,
the
test
suite
and
the
live
editor
will
continue,
they
are
believed
to
be
mature
enough
to
be
integrated
into
a
non-production
system
at
this
point
in
time
with
the
expectation
that
they
could
be
used
in
a
production
system
within
the
next
three
two
months.
The
following
features
are
at
risk
and
may
be
removed:
Support
for
@base:
null
Confusion
related
to
context-sensitivity
of
@type
Lists
of
lists
and
partial
list
conversion
from
RDF
Allow
blank
nodes
to
be
used
as
properties
Changes
since
the
11 April 2013
Last
Call
Working
Draft
10 September 2013
Candidate
Recommendation
:
+json
@type
This
document
was
published
by
the
RDF
Working
Group
as
a
Candidate
Proposed
Recommendation.
This
document
is
intended
to
become
a
W3C
Recommendation.
If
you
wish
The
W3C
Membership
and
other
interested
parties
are
invited
to
make
comments
regarding
this
document,
please
review
the
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and
send
them
comments
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public-rdf-comments@w3.org
(
subscribe
,
archives
).
W3C
publishes
a
Candidate
Recommendation
to
indicate
)
through
05
December
2013.
Advisory
Committee
Representatives
should
consult
their
WBS
questionnaires
.
Note
that
the
document
is
believed
to
be
stable
and
to
encourage
implementation
by
the
developer
community.
This
Candidate
Recommendation
is
substantive
technical
comments
were
expected
to
advance
to
Proposed
Recommendation
no
earlier
than
01
October
during
the
Last
Call
review
period
that
ended
10
May
2013.
All
comments
are
welcome.
Publication
as
a
Candidate
Proposed
Recommendation
does
not
imply
endorsement
by
the
W3C
Membership.
This
is
a
draft
document
and
may
be
updated,
replaced
or
obsoleted
by
other
documents
at
any
time.
It
is
inappropriate
to
cite
this
document
as
other
than
work
in
progress.
Before
this
specification
may
exit
the
Candidate
Recommendation
phase,
at
least
two
independent
implementations
must
pass
each
test,
although
no
single
implementation
must
pass
every
test.
The
working
group
will
decide
when
the
test
suite
is
of
sufficient
quality
to
test
interoperability
and
will
produce
an
implementation
report
hosted
together
with
the
test
suite.
This
document
was
produced
by
a
group
operating
under
the
5
February
2004
W3C
Patent
Policy
.
W3C
maintains
a
public
list
of
any
patent
disclosures
made
in
connection
with
the
deliverables
of
the
group;
that
page
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for
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An
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which
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believes
contains
Essential
Claim(s)
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accordance
with
section
6
of
the
W3C
Patent
Policy
.
This section is non-normative.
Linked Data [ LINKED-DATA ] is a way to create a network of standards-based machine interpretable data across different documents and Web sites. It allows an application to start at one piece of Linked Data, and follow embedded links to other pieces of Linked Data that are hosted on different sites across the Web.
JSON-LD is a lightweight syntax to serialize Linked Data in JSON [ RFC4627 ]. Its design allows existing JSON to be interpreted as Linked Data with minimal changes. JSON-LD is primarily intended to be a way to use Linked Data in Web-based programming environments, to build interoperable Web services, and to store Linked Data in JSON-based storage engines. Since JSON-LD is 100% compatible with JSON, the large number of JSON parsers and libraries available today can be reused. In addition to all the features JSON provides, JSON-LD introduces:
JSON-LD is designed to be usable directly as JSON, with no knowledge of RDF [ RDF11-CONCEPTS ]. It is also designed to be usable as RDF, if desired, for use with other Linked Data technologies like SPARQL. Developers who require any of the facilities listed above or need to serialize an RDF Graph or RDF Dataset in a JSON-based syntax will find JSON-LD of interest. People intending to use JSON-LD with RDF tools will find it can be used as another RDF syntax, like Turtle [ TURTLE ]. Complete details of how JSON-LD relates to RDF are in section 9. Relationship to RDF .
The syntax is designed to not disturb already deployed systems running on JSON, but provide a smooth upgrade path from JSON to JSON-LD. Since the shape of such data varies wildly, JSON-LD features mechanisms to reshape documents into a deterministic structure which simplifies their processing.
This section is non-normative.
This document is a detailed specification for a serialization of Linked Data in JSON. The document is primarily intended for the following audiences:
A companion document, the JSON-LD Processing Algorithms and API specification [ JSON-LD-API ], specifies how to work with JSON-LD at a higher level by providing a standard library interface for common JSON-LD operations.
To understand the basics in this specification you must first be familiar with JSON, which is detailed in [ RFC4627 ].
This document almost exclusively uses the term IRI ( Internationalized Resource Indicator ) when discussing hyperlinks. Many Web developers are more familiar with the URL ( Uniform Resource Locator ) terminology. The document also uses, albeit rarely, the URI ( Uniform Resource Indicator ) terminology. While these terms are often used interchangeably among technical communities, they do have important distinctions from one another and the specification goes to great lengths to try and use the proper terminology at all times.
This section is non-normative.
JSON-LD satisfies the following design goals:
@context
and
@id
)
to
use
the
basic
functionality
in
JSON-LD.
This document uses the following terms as defined in JSON [ RFC4627 ]. Refer to the JSON Grammar section in [ RFC4627 ] for formal definitions.
@context
where
the
value
is
null
explicitly
decouples
a
term
's
association
with
an
IRI
.
A
key-value
pair
in
the
body
of
a
JSON-LD
document
whose
value
is
null
has
the
same
meaning
as
if
the
key-value
pair
was
not
defined.
If
@value
,
@list
,
or
@set
is
set
to
null
in
expanded
form,
then
the
entire
JSON
object
is
ignored.
This section is non-normative.
Generally speaking, the data model used for JSON-LD is a labeled, directed graph . The graph contains nodes , which are connected by edges . A node is typically data such as a string , number , typed values (like dates and times) or an IRI . There is also a special class of node called a blank node , which is typically used to express data that does not have a global identifier like an IRI . Blank nodes are identified using a blank node identifier . This simple data model is incredibly flexible and powerful, capable of modeling almost any kind of data. For a deeper explanation of the data model, see section 7. Data Model .
Developers who are familiar with Linked Data technologies will recognize the data model as the RDF Data Model. To dive deeper into how JSON-LD and RDF are related, see section 9. Relationship to RDF .
JSON-LD specifies a number of syntax tokens and keywords that are a core part of the language:
@context
@context
keyword
is
described
in
detail
in
section
5.1
The
Context
.
@id
@value
@language
@type
@container
@list
@set
@reverse
@index
@base
@vocab
@type
with
a
common
prefix
IRI
.
This
keyword
is
described
in
section
6.2
Default
Vocabulary
.
@graph
:
All keys, keywords , and values in JSON-LD are case-sensitive.
This specification describes the conformance criteria for JSON-LD documents. This criteria is relevant to authors and authoring tool implementers. As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
A JSON-LD document complies with this specification if it follows the normative statements in appendix 8. JSON-LD Grammar . JSON documents can be interpreted as JSON-LD by following the normative statements in section 6.8 Interpreting JSON as JSON-LD . For convenience, normative statements for documents are often phrased as statements on the properties of the document.
The key words MUST , MUST NOT , REQUIRED , SHALL , SHALL NOT , SHOULD , SHOULD NOT , RECOMMENDED , NOT RECOMMENDED , MAY , and OPTIONAL in this specification have the meaning defined in [ RFC2119 ].
This section is non-normative.
JSON [ RFC4627 ] is a lightweight, language-independent data interchange format. It is easy to parse and easy to generate. However, it is difficult to integrate JSON from different sources as the data may contain keys that conflict with other data sources. Furthermore, JSON has no built-in support for hyperlinks, which are a fundamental building block on the Web. Let's start by looking at an example that we will be using for the rest of this section:
{ "name": "Manu Sporny", "homepage": "http://manu.sporny.org/", "image": "http://manu.sporny.org/images/manu.png" }
It's
obvious
to
humans
that
the
data
is
about
a
person
whose
name
is
"Manu
Sporny"
and
that
the
homepage
property
contains
the
URL
of
that
person's
homepage.
A
machine
doesn't
have
such
an
intuitive
understanding
and
sometimes,
even
for
humans,
it
is
difficult
to
resolve
ambiguities
in
such
representations.
This
problem
can
be
solved
by
using
unambiguous
identifiers
to
denote
the
different
concepts
instead
of
tokens
such
as
"name",
"homepage",
etc.
Linked
Data,
and
the
Web
in
general,
uses
IRIs
(Internationalized
Resource
Identifiers
as
described
in
[
RFC3987
])
for
unambiguous
identification.
The
idea
is
to
use
IRIs
to
assign
unambiguous
identifiers
to
data
that
may
be
of
use
to
other
developers.
It
is
useful
for
terms
,
like
name
and
homepage
,
to
expand
to
IRIs
so
that
developers
don't
accidentally
step
on
each
other's
terms.
Furthermore,
developers
and
machines
are
able
to
use
this
IRI
(by
using
a
web
browser,
for
instance)
to
go
to
the
term
and
get
a
definition
of
what
the
term
means.
This
process
is
known
as
IRI
dereferencing.
Leveraging the popular schema.org vocabulary , the example above could be unambiguously expressed as follows:
{ "http://schema.org/name": "Manu Sporny", "http://schema.org/url": { "@id": "http://manu.sporny.org/" }, ← The '@id' keyword means 'This value is an identifier that is an IRI' "http://schema.org/image": { "@id": "http://manu.sporny.org/images/manu.png" } }
In
the
example
above,
every
property
is
unambiguously
identified
by
an
IRI
and
all
values
representing
IRIs
are
explicitly
marked
as
such
by
the
@id
keyword
.
While
this
is
a
valid
JSON-LD
document
that
is
very
specific
about
its
data,
the
document
is
also
overly
verbose
and
difficult
to
work
with
for
human
developers.
To
address
this
issue,
JSON-LD
introduces
the
notion
of
a
context
as
described
in
the
next
section.
This section is non-normative.
When two people communicate with one another, the conversation takes place in a shared environment, typically called "the context of the conversation". This shared context allows the individuals to use shortcut terms, like the first name of a mutual friend, to communicate more quickly but without losing accuracy. A context in JSON-LD works in the same way. It allows two applications to use shortcut terms to communicate with one another more efficiently, but without losing accuracy.
Simply speaking, a context is used to map terms to IRIs . Terms are case sensitive and any valid string that is not a reserved JSON-LD keyword can be used as a term .
For the sample document in the previous section, a context would look something like this:
{ "@context": {"name": "http://schema.org/name","name": "http://schema.org/name", ← This means that 'name' is shorthand for 'http://schema.org/name' "image": {"@id": "http://schema.org/image", "@type": "@id""@id": "http://schema.org/image", ← This means that 'image' is shorthand for 'http://schema.org/image' "@type": "@id" ← This means that a string value associated with 'image' should be interpreted as an identifier that is an IRI }, "homepage": {"@id": "http://schema.org/url", "@type": "@id""@id": "http://schema.org/url", ← This means that 'homepage' is shorthand for 'http://schema.org/url' "@type": "@id" ← This means that a string value associated with 'homepage' should be interpreted as an identifier that is an IRI } } }
As the context above shows, the value of a term definition can either be a simple string, mapping the term to an IRI , or a JSON object .
When
a
JSON
object
is
associated
with
a
term,
it
is
called
an
expanded
term
definition
.
The
example
above
specifies
that
the
values
of
image
and
homepage
,
if
they
are
strings,
are
to
be
interpreted
as
IRIs
.
Expanded
term
definitions
also
allow
terms
to
be
used
for
index
maps
and
to
specify
whether
array
values
are
to
be
interpreted
as
sets
or
lists
.
Expanded
term
definitions
may
be
defined
using
absolute
or
compact
IRIs
as
keys,
which
is
mainly
used
to
associate
type
or
language
information
with
an
absolute
or
compact
IRI
.
Contexts
can
either
be
directly
embedded
into
the
document
or
be
referenced.
Assuming
the
context
document
in
the
previous
example
can
be
retrieved
at
http://json-ld.org/contexts/person.jsonld
,
it
can
be
referenced
by
adding
a
single
line
and
allows
a
JSON-LD
document
to
be
expressed
much
more
concisely
as
shown
in
the
example
below:
{
"@context": "http://json-ld.org/contexts/person.jsonld",
"name": "Manu Sporny",
"homepage": "http://manu.sporny.org/",
"image": "http://manu.sporny.org/images/manu.png"
}
The
referenced
context
not
only
specifies
how
the
terms
map
to
IRIs
in
the
Schema.org
vocabulary
but
also
specifies
that
string
values
associated
with
the
homepage
and
image
property
can
be
interpreted
as
an
IRI
(
"@type":
"@id"
,
see
section
5.2
IRIs
for
more
details).
This
information
allows
developers
to
re-use
each
other's
data
without
having
to
agree
to
how
their
data
will
interoperate
on
a
site-by-site
basis.
External
JSON-LD
context
documents
may
contain
extra
information
located
outside
of
the
@context
key,
such
as
documentation
about
the
terms
declared
in
the
document.
Information
contained
outside
of
the
@context
value
is
ignored
when
the
document
is
used
as
an
external
JSON-LD
context
document.
JSON documents can be interpreted as JSON-LD without having to be modified by referencing a context via an HTTP Link Header as described in section 6.8 Interpreting JSON as JSON-LD . It is also possible to apply a custom context using the JSON-LD API [ JSON-LD-API ].
In JSON-LD documents , contexts may also be specified inline. This has the advantage that documents can be processed even in the absence of a connection to the Web. Ultimately, this is a modeling decision and different use cases may require different handling.
{
"@context":
{
"name": "http://schema.org/name",
"image": {
"@id": "http://schema.org/image",
"@type": "@id"
},
"homepage": {
"@id": "http://schema.org/url",
"@type": "@id"
}
},
"name": "Manu Sporny",
"homepage": "http://manu.sporny.org/",
"image": "http://manu.sporny.org/images/manu.png"
}
This section only covers the most basic features of the JSON-LD Context. More advanced features related to the JSON-LD Context are covered in section 6. Advanced Concepts .
This section is non-normative.
IRIs (Internationalized Resource Identifiers [ RFC3987 ]) are fundamental to Linked Data as that is how most nodes and properties are identified. In JSON-LD, IRIs may be represented as an absolute IRI or a relative IRI . An absolute IRI is defined in [ RFC3987 ] as containing a scheme along with path and optional query and fragment segments. A relative IRI is an IRI that is relative to some other absolute IRI . In JSON-LD all relative IRIs are resolved relative to the base IRI .
A
string
is
interpreted
as
an
IRI
when
it
is
the
value
of
an
@id
member:
{ ..."homepage": { "": "http://example.com/" }"homepage": { "@id": "http://example.com/" } ... }
Values
that
are
interpreted
as
IRIs
,
can
also
be
expressed
as
relative
IRIs
.
For
example,
assuming
that
the
following
document
is
located
at
http://example.com/about/
,
the
relative
IRI
../
would
expand
to
http://example.com/
(for
more
information
on
where
relative
IRIs
can
be
used,
please
refer
to
section
8.
JSON-LD
Grammar
).
{ ..."homepage": { "": "../" }"homepage": { "@id": "../" } ... }
Absolute IRIs can be expressed directly in the key position like so:
{ ..."": "Manu Sporny","http://schema.org/name": "Manu Sporny", ... }
In
the
example
above,
the
key
http://schema.org/name
is
interpreted
as
an
absolute
IRI
.
Term-to- IRI expansion occurs if the key matches a term defined within the active context :
{ "@context": {"""name": "http://schema.org/name" },"": "Manu Sporny","name": "Manu Sporny", "status": "trollin'" }
JSON
keys
that
do
not
expand
to
an
IRI
,
such
as
status
in
the
example
above,
are
not
Linked
Data
and
thus
ignored
when
processed.
If
type
coercion
rules
are
specified
in
the
@context
for
a
particular
term
or
property
IRI
,
an
IRI
is
generated:
{
"@context":
{
...
"homepage":
{
"@id": "http://schema.org/url",
"@type": "@id"
}
...
}
...
"homepage": "http://manu.sporny.org/",
...
}
In
the
example
above,
since
the
value
http://manu.sporny.org/
is
expressed
as
a
JSON
string
,
the
type
coercion
rules
will
transform
the
value
into
an
IRI
when
processing
the
data.
See
section
6.5
Type
Coercion
for
more
details
about
this
feature.
In summary, IRIs can be expressed in a variety of different ways in JSON-LD:
@id
or
@type
.
@type
key
that
is
set
to
a
value
of
@id
or
@vocab
.
This section only covers the most basic features associated with IRIs in JSON-LD. More advanced features related to IRIs are covered in section 6. Advanced Concepts .
This section is non-normative.
To be able to externally reference nodes in a graph , it is important that nodes have an identifier. IRIs are a fundamental concept of Linked Data, for nodes to be truly linked, dereferencing the identifier should result in a representation of that node . This may allow an application to retrieve further information about a node .
In
JSON-LD,
a
node
is
identified
using
the
@id
keyword
:
{ "@context": { ... "name": "http://schema.org/name" },,"@id": "http://me.markus-lanthaler.com/", "name": "Markus Lanthaler", ... }
The
example
above
contains
a
node
object
identified
by
the
IRI
http://me.markus-lanthaler.com/
.
This section only covers the most basic features associated with node identifiers in JSON-LD. More advanced features related to node identifiers are covered in section 6. Advanced Concepts .
This section is non-normative.
The
type
of
a
particular
node
can
be
specified
using
the
@type
keyword
.
In
Linked
Data,
types
are
uniquely
identified
with
an
IRI
.
{ ... "@id": "http://example.org/places#BrewEats","","@type": "http://schema.org/Restaurant", ... }
A node can be assigned more than one type by using an array :
{ ... "@id": "http://example.org/places#BrewEats",""@type": [ "http://schema.org/Restaurant", "http://schema.org/Brewery" ], ... }
The
value
of
a
@type
key
may
also
be
a
term
defined
in
the
active
context
:
{ "@context": { ..."Restaurant": "http://schema.org/Restaurant", "Brewery": "http://schema.org/Brewery" } "@id": "http://example.org/places#BrewEats",,"@type": [ "Restaurant", "Brewery" ], ... }
This
section
only
covers
the
most
basic
features
associated
with
types
in
JSON-LD.
More
advanced
features
related
It
is
worth
noting
that
the
@type
keyword
is
not
only
used
to
types
are
covered
specify
the
type
of
a
node
but
also
to
express
typed
values
(as
described
in
section
6.
Advanced
Concepts
6.4
Typed
Values
)
and
to
type
coerce
values
(as
described
in
section
6.5
Type
Coercion
).
Specifically,
@type
cannot
be
used
in
a
context
to
define
a
node's
type.
For
a
detailed
description
of
the
differences,
please
refer
to
section
6.4
Typed
Values
.
JSON-LD has a number of features that provide functionality above and beyond the core functionality described above. The following section describes this advanced functionality in more detail.
This section is non-normative.
JSON-LD
allows
IRI
s
to
be
specified
in
a
relative
form
which
is
resolved
against
the
document
base
according
section
5.1
Establishing
a
Base
URI
of
[
RFC3986
].
The
base
IRI
may
be
explicitly
set
with
a
context
using
the
@base
keyword.
For
example,
if
a
JSON-LD
document
was
retrieved
from
http://example.com/document.jsonld
,
relative
IRIs
would
resolve
against
that
IRI
:
{ "@context": { "label": "http://www.w3.org/2000/01/rdf-schema#label" },,"@id": "", "label": "Just a simple document" }
This
document
uses
an
empty
@id
,
which
resolves
to
the
document
base.
However,
if
the
document
is
moved
to
a
different
location,
the
IRI
would
change.
To
prevent
this
without
having
to
use
an
absolute
IRI
,
a
context
may
define
a
@base
mapping,
to
overwrite
the
base
IRI
for
the
document.
{ "@context": {"@base": "http://example.com/document.jsonld" }, "@id": "", "label": "Just a simple document" }
Setting
@base
to
null
will
prevent
relative
IRIs
to
be
expanded
to
absolute
IRIs
.
Please
note
that
the
@base
will
be
ignored
if
used
in
external
contexts.
This section is non-normative.
At
times,
all
properties
and
types
may
come
from
the
same
vocabulary.
JSON-LD's
@vocab
keyword
allows
an
author
to
set
a
common
prefix
to
be
used
for
all
properties
and
types
that
do
not
match
a
term
and
are
neither
a
compact
IRI
nor
an
absolute
IRI
(i.e.,
they
do
not
contain
a
colon).
{ "@context": {"@vocab": "http://schema.org/" } "@id": "http://example.org/places#BrewEats","@type": , : "Brew Eats""@type": "Restaurant", "name": "Brew Eats" ... }
If
@vocab
is
used
but
certain
keys
in
an
object
should
not
be
expanded
using
the
vocabulary
IRI
,
a
term
can
be
explicitly
set
to
null
in
the
context
.
For
instance,
in
the
example
below
the
databaseId
member
would
not
expand
to
an
IRI
.
{ "@context": { "@vocab": "http://schema.org/","databaseId": null }, "@id": "http://example.org/places#BrewEats", "@type": "Restaurant", "name": "Brew Eats",: "23987520""databaseId": "23987520" }
This section is non-normative.
A
compact
IRI
is
a
way
of
expressing
an
IRI
using
a
prefix
and
suffix
separated
by
a
colon
(
:
).
The
prefix
is
a
term
taken
from
the
active
context
and
is
a
short
string
identifying
a
particular
IRI
in
a
JSON-LD
document.
For
example,
the
prefix
foaf
may
be
used
as
a
short
hand
for
the
Friend-of-a-Friend
vocabulary,
which
is
identified
using
the
IRI
http://xmlns.com/foaf/0.1/
.
A
developer
may
append
any
of
the
FOAF
vocabulary
terms
to
the
end
of
the
prefix
to
specify
a
short-hand
version
of
the
absolute
IRI
for
the
vocabulary
term.
For
example,
foaf:name
would
be
expanded
to
the
IRI
http://xmlns.com/foaf/0.1/name
.
{ "@context": {"""foaf": "http://xmlns.com/foaf/0.1/" ... },"@type": "" "": "Dave Longley","@type": "foaf:Person" "foaf:name": "Dave Longley", ... }
In
the
example
above,
foaf:name
expands
to
the
IRI
http://xmlns.com/foaf/0.1/name
and
foaf:Person
expands
to
http://xmlns.com/foaf/0.1/Person
.
Prefixes
are
expanded
when
the
form
of
the
value
is
a
compact
IRI
represented
as
a
prefix:suffix
combination,
the
prefix
matches
a
term
defined
within
the
active
context
,
and
the
suffix
does
not
begin
with
two
slashes (
slashes (
//
).
The
compact
IRI
is
expanded
by
concatenating
the
IRI
mapped
to
the
prefix
to
the
(possibly
empty)
suffix
.
If
the
prefix
is
not
defined
in
the
active
context
,
or
the
suffix
begins
with
two
slashes
(such
as
in
http://example.com
),
the
value
is
interpreted
as
absolute
IRI
instead.
If
the
prefix
is
an
underscore
(
_
),
the
value
is
interpreted
as
blank
node
identifier
instead.
It's also possible to use compact IRIs within the context as shown in the following example:
{ "@context": { "xsd": "http://www.w3.org/2001/XMLSchema#",, : { "@type": "@id" }, "picture": { "@id": , "@type": "@id" }"foaf": "http://xmlns.com/foaf/0.1/", "foaf:homepage": { "@type": "@id" }, "picture": { "@id": "foaf:depiction", "@type": "@id" } }, "@id": "http://me.markus-lanthaler.com/", "@type": "foaf:Person", "foaf:name": "Markus Lanthaler", "foaf:homepage": "http://www.markus-lanthaler.com/", "picture": "http://twitter.com/account/profile_image/markuslanthaler" }
This section is non-normative.
A value with an associated type, also known as a typed value , is indicated by associating a value with an IRI which indicates the value's type. Typed values may be expressed in JSON-LD in three ways:
@type
keyword
when
defining
a
term
within
a
@context
section.
The
first
example
uses
the
@type
keyword
to
associate
a
type
with
a
particular
term
in
the
@context
:
{
"@context":
{
"modified":
{
"@id": "http://purl.org/dc/terms/modified",
"@type": "http://www.w3.org/2001/XMLSchema#dateTime"
}
},
...
"@id": "http://example.com/docs/1",
"modified": "2010-05-29T14:17:39+02:00",
...
}
The
modified
key's
value
above
is
automatically
type
coerced
to
a
dateTime
value
because
of
the
information
specified
in
the
@context
.
A
JSON-LD
processor
will
interpret
the
example
above
as
follows:
Subject | Property | Value | Value Type |
---|---|---|---|
http://example.com/docs/1 | http://purl.org/dc/terms/modified | 2010-05-29T14:17:39+02:00 | http://www.w3.org/2001/XMLSchema#dateTime |
The second example uses the expanded form of setting the type information in the body of a JSON-LD document:
{ "@context": { "modified": { "@id": "http://purl.org/dc/terms/modified" } }, ... "modified":{{ "@value": "2010-05-29T14:17:39+02:00", "@type": "http://www.w3.org/2001/XMLSchema#dateTime" } ... }
Both
examples
above
would
generate
the
value
2010-05-29T14:17:39+02:00
with
the
type
http://www.w3.org/2001/XMLSchema#dateTime
.
Note
that
it
is
also
possible
to
use
a
term
or
a
compact
IRI
to
express
the
value
of
a
type.
The
@type
keyword
is
also
used
to
associate
a
type
with
a
node
.
The
concept
of
a
node
type
and
a
value
type
are
different.
Generally
speaking,
a
A
node
type
specifies
the
type
of
thing
that
is
being
described,
like
a
person,
place,
event,
or
web
page.
A
value
type
specifies
the
data
type
of
a
particular
value,
such
as
an
integer,
a
floating
point
number,
or
a
date.
{ ... "@id": "http://example.org/posts#TripToWestVirginia",, <- This is a node type"@type": "http://schema.org/BlogPosting", ← This is a node type "modified": { "@value": "2010-05-29T14:17:39+02:00",<- This is a value type"@type": "http://www.w3.org/2001/XMLSchema#dateTime" ← This is a value type } ... }
The
first
use
of
@type
associates
a
node
type
(
http://schema.org/BlogPosting
)
with
the
node
,
which
is
expressed
using
the
@id
keyword
.
The
second
use
of
@type
associates
a
value
type
(
http://www.w3.org/2001/XMLSchema#dateTime
)
with
the
value
expressed
using
the
@value
keyword
.
As
a
general
rule,
when
@value
and
@type
are
used
in
the
same
JSON
object
,
the
@type
keyword
is
expressing
a
value
type
.
Otherwise,
the
@type
keyword
is
expressing
a
node
type
.
The
example
above
expresses
the
following
data:
Subject | Property | Value | Value Type |
---|---|---|---|
http://example.org/posts#TripToWestVirginia | http://www.w3.org/1999/02/22-rdf-syntax-ns#type | http://schema.org/BlogPosting | - |
http://example.org/posts#TripToWestVirginia | http://purl.org/dc/terms/modified | 2010-05-29T14:17:39+02:00 | http://www.w3.org/2001/XMLSchema#dateTime |
This section is non-normative.
JSON-LD supports the coercion of values to particular data types. Type coercion allows someone deploying JSON-LD to coerce the incoming or outgoing values to the proper data type based on a mapping of data type IRIs to terms . Using type coercion, value representation is preserved without requiring the data type to be specified with each piece of data.
Type
coercion
is
specified
within
an
expanded
term
definition
using
the
@type
key.
The
value
of
this
key
expands
to
an
IRI
.
Alternatively,
the
keywords
@id
or
@vocab
may
be
used
as
value
to
indicate
that
within
the
body
of
a
JSON-LD
document,
a
string
value
of
a
term
coerced
to
@id
or
@vocab
is
to
be
interpreted
as
an
IRI
.
The
difference
between
@id
and
@vocab
is
how
values
are
expanded
to
absolute
IRIs
.
@vocab
first
tries
to
expand
the
value
by
interpreting
it
as
term
.
If
no
matching
term
is
found
in
the
active
context
,
it
tries
to
expand
it
as
compact
IRI
or
absolute
IRI
if
there's
a
colon
in
the
value;
otherwise,
it
will
expand
the
value
using
the
active
context's
vocabulary
mapping,
if
present,
or
by
interpreting
it
as
relative
IRI
.
Values
coerced
to
@id
in
contrast
are
expanded
as
compact
IRI
or
absolute
IRI
if
a
colon
is
present;
otherwise,
they
are
interpreted
as
relative
IRI
.
Terms
or
compact
IRIs
used
as
the
value
of
a
@type
key
may
be
defined
within
the
same
context.
This
means
that
one
may
specify
a
term
like
xsd
and
then
use
xsd:integer
within
the
same
context
definition.
The example below demonstrates how a JSON-LD author can coerce values to typed values and IRIs .
{ "@context": { "xsd": "http://www.w3.org/2001/XMLSchema#", "name": "http://xmlns.com/foaf/0.1/name", "age":{{ "@id": "http://xmlns.com/foaf/0.1/age", "@type": "xsd:integer" }, "homepage":{{ "@id": "http://xmlns.com/foaf/0.1/homepage", "@type": "@id" } }, "@id": "http://example.com/people#john", "name": "John Smith","age": ,"age": "41", "homepage":[[ "http://personal.example.org/", "http://work.example.com/jsmith/" ] }
The example shown above would generate the following data.
Subject | Property | Value | Value Type |
---|---|---|---|
http://example.com/people#john | http://xmlns.com/foaf/0.1/name | John Smith |
|
http://example.com/people#john | http://xmlns.com/foaf/0.1/age | 41 | http://www.w3.org/2001/XMLSchema#integer |
http://example.com/people#john | http://xmlns.com/foaf/0.1/homepage | http://personal.example.org/ | IRI |
http://work.example.com/jsmith/ | IRI |
Terms may also be defined using absolute IRIs or compact IRIs . This allows coercion rules to be applied to keys which are not represented as a simple term . For example:
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/","":"foaf:age": {,"@id": "http://xmlns.com/foaf/0.1/age", "@type": "xsd:integer" },"":"http://xmlns.com/foaf/0.1/homepage": { "@type": "@id" } }, "foaf:name": "John Smith","": "41", "":"foaf:age": "41", "http://xmlns.com/foaf/0.1/homepage": [ "http://personal.example.org/", "http://work.example.com/jsmith/" ] }
In
this
case
the
@id
definition
in
the
term
definition
is
optional.
If
it
does
exist,
the
compact
IRI
or
IRI
representing
the
term
will
always
be
expanded
to
IRI
defined
by
the
@id
key—regardless
of
whether
a
prefix
is
defined
or
not.
Type
coercion
is
always
performed
using
the
unexpanded
value
of
the
key.
In
the
example
above,
that
means
that
type
coercion
is
done
looking
for
foaf:age
in
the
active
context
and
not
for
the
corresponding,
expanded
IRI
http://xmlns.com/foaf/0.1/age
.
Keys
in
the
context
are
treated
as
terms
for
the
purpose
of
expansion
and
value
coercion.
At
times,
this
may
result
in
multiple
representations
for
the
same
expanded
IRI
.
For
example,
one
could
specify
that
dog
and
cat
both
expanded
to
http://example.com/vocab#animal
.
Doing
this
could
be
useful
for
establishing
different
type
coercion
or
language
specification
rules.
It
also
allows
a
compact
IRI
(or
even
an
absolute
IRI
)
to
be
defined
as
something
else
entirely.
For
example,
one
could
specify
that
the
term
http://example.org/zoo
should
expand
to
http://example.org/river
,
but
this
usage
is
discouraged
because
it
would
lead
to
a
great
deal
of
confusion
among
developers
attempting
to
understand
the
JSON-LD
document.
This section is non-normative.
Embedding is a JSON-LD feature that allows an author to use node objects as property values. This is a commonly used mechanism for creating a parent-child relationship between two nodes .
The example shows two nodes related by a property from the first node:
{ ... "name": "Manu Sporny","":"knows": {"", "","@type": "Person", "name": "Gregg Kellogg", } ... }
A node object , like the one used above, may be used in any value position in the body of a JSON-LD document.
This section is non-normative.
Section 5.1 The Context introduced the basics of what makes JSON-LD work. This section expands on the basic principles of the context and demonstrates how more advanced use cases can be achieved using JSON-LD.
In general, contexts may be used at any time a JSON object is defined. The only time that one cannot express a context is inside a context definition itself. For example, a JSON-LD document may use more than one context at different points in a document:
[ {"@context": "http://example.org/contexts/person.jsonld", "name": "Manu Sporny", "homepage": "http://manu.sporny.org/", "depiction": "http://twitter.com/account/profile_image/manusporny" }, {"@context": "http://example.org/contexts/place.jsonld", "name": "The Empire State Building", "description": "The Empire State Building is a 102-story landmark in New York City.", "geo": { "latitude": "40.75", "longitude": "73.98" } } ]
Duplicate context terms are overridden using a most-recently-defined-wins mechanism.
{ "@context": { "name": "http://example.com/person#name, "details": "http://example.com/person#details" }","": "Markus Lanthaler","name": "Markus Lanthaler", ... "details": {"@context":"@context": { "name": "http://example.com/organization#name" },"": "Graz University of Technology""name": "Graz University of Technology" } }
In
the
example
above,
the
name
term
is
overridden
in
the
more
deeply
nested
details
structure.
Note
that
this
is
rarely
a
good
authoring
practice
and
is
typically
used
when
working
with
legacy
applications
that
depend
on
a
specific
structure
of
the
JSON
object
.
If
a
term
is
redefined
within
a
context,
all
previous
rules
associated
with
the
previous
definition
are
removed.
If
a
term
is
redefined
to
null
,
the
term
is
effectively
removed
from
the
list
of
terms
defined
in
the
active
context
.
Multiple
contexts
may
be
combined
using
an
array
,
which
is
processed
in
order.
The
set
of
contexts
defined
within
a
specific
JSON
object
are
referred
to
as
local
contexts
.
The
active
context
refers
to
the
accumulation
of
local
contexts
that
are
in
scope
at
a
specific
point
within
the
document.
Setting
a
local
context
to
null
effectively
resets
the
active
context
to
an
empty
context.
The
following
example
specifies
an
external
context
and
then
layers
an
embedded
context
on
top
of
the
external
context:
{ "@context": [ "http://json-ld.org/contexts/person.jsonld", { "pic": "http://xmlns.com/foaf/0.1/depiction" } ], "name": "Manu Sporny", "homepage": "http://manu.sporny.org/","pic": "http://twitter.com/account/profile_image/manusporny" }
When possible, the context definition should be put at the top of a JSON-LD document. This makes the document easier to read and might make streaming parsers more efficient. Documents that do not have the context at the top are still conformant JSON-LD.
To
avoid
forward-compatibility
issues,
terms
starting
with
an
an
@
character
are
to
be
avoided
as
they
might
be
used
as
keywords
in
future
versions
of
JSON-LD.
Terms
starting
with
an
an
@
character
that
are
not
JSON-LD
1.0
keywords
are
treated
as
any
other
term,
i.e.,
they
are
ignored
unless
mapped
to
an
IRI
.
Furthermore,
the
use
of
empty
terms
(
""
)
is
not
allowed
as
not
all
programming
languages
are
able
to
handle
empty
JSON
keys.
Ordinary
JSON
documents
can
be
interpreted
as
JSON-LD
by
referencing
a
JSON-LD
context
document
in
an
HTTP
Link
Header.
Doing
so
allows
JSON
to
be
unambiguously
machine-readable
without
requiring
developers
to
drastically
change
their
documents
and
provides
an
upgrade
path
for
existing
infrastructure
without
breaking
existing
clients
that
rely
on
the
application/json
media
type
or
a
media
type
with
a
+json
suffix
as
defined
in
[
RFC6839
].
In
order
to
use
an
external
context
with
an
ordinary
JSON
document,
an
author
MUST
specify
an
IRI
to
a
valid
JSON-LD
document
in
an
HTTP
Link
Header
[
RFC5988
]
using
the
http://www.w3.org/ns/json-ld#context
link
relation.
The
referenced
document
MUST
have
a
top-level
JSON
object
.
The
@context
subtree
within
that
object
is
added
to
the
top-level
JSON
object
of
the
referencing
document.
If
an
array
is
at
the
top-level
of
the
referencing
document
and
its
items
are
JSON
objects
,
the
@context
subtree
is
added
to
all
array
items.
All
extra
information
located
outside
of
the
@context
subtree
in
the
referenced
document
MUST
be
discarded.
Effectively
this
means
that
the
active
context
is
initialized
with
the
referenced
external
context
.
A
response
MUST
NOT
contain
more
than
one
HTTP
Link
Header
[
RFC5988
]
using
the
http://www.w3.org/ns/json-ld#context
link
relation.
The following example demonstrates the use of an external context with an ordinary JSON document:
GET /ordinary-json-document.json HTTP/1.1 Host: example.com Accept: application/ld+json,application/json,*/*;q=0.1 ==================================== HTTP/1.1 200 OK ...Content-Type:Content-Type: application/json Link: <http://json-ld.org/contexts/person.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json" { "name": "Markus Lanthaler", "homepage": "http://www.markus-lanthaler.com/", "image": "http://twitter.com/account/profile_image/markuslanthaler" }
Please
note
that
JSON-LD
documents
served
with
the
application/ld+json
media
type
MUST
have
all
context
information,
including
references
to
external
contexts,
within
the
body
of
the
document.
Contexts
linked
via
a
http://www.w3.org/ns/json-ld#context
HTTP
Link
Header
MUST
be
ignored
for
such
documents.
This section is non-normative.
At
times,
it
is
important
to
annotate
a
string
with
its
language.
In
JSON-LD
this
is
possible
in
a
variety
of
ways.
First,
it
is
possible
to
define
a
default
language
for
a
JSON-LD
document
by
setting
the
@language
key
in
the
context
:
{ "@context": { ... "@language": "ja" },"name": , "occupation":"name": "花澄", "occupation": "科学者" }
The
example
above
would
associate
the
ja
language
code
with
the
two
strings
花澄
and
科学者
.
Languages
codes
are
defined
in
[
BCP47
].
The
default
language
applies
to
all
string
values
that
are
not
type
coerced
.
To
clear
the
default
language
for
a
subtree,
@language
can
be
set
to
null
in
a
local
context
as
follows:
{ "@context": { ... "@language": "ja" }, "name": "花澄", "details": {"@context": {"@context": { "@language": null }, "occupation": "Ninja" } }
Second, it is possible to associate a language with a specific term using an expanded term definition :
{ "@context": { ... "ex": "http://example.com/vocab/", "@language": "ja","name": { "@id": "ex:name", },"name": { "@id": "ex:name", "@language": null }, "occupation": { "@id": "ex:occupation" },"occupation_en": { "@id": "ex:occupation", }, "occupation_cs": { "@id": "ex:occupation", }"occupation_en": { "@id": "ex:occupation", "@language": "en" }, "occupation_cs": { "@id": "ex:occupation", "@language": "cs" } },"name": "Yagyū Muneyoshi","name": "Yagyū Muneyoshi", "occupation": "忍者", "occupation_en": "Ninja", "occupation_cs": "Nindža", ... }
The
example
above
would
associate
忍者
with
the
specified
default
language
code
ja
,
Ninja
with
the
language
code
en
,
and
Nindža
with
the
language
code
cs
.
The
value
of
name
,
Yagyū
Muneyoshi
wouldn't
be
associated
with
any
language
code
since
@language
was
reset
to
null
in
the
expanded
term
definition
.
Language associations are only applied to plain strings . Typed values or values that are subject to type coercion are not language tagged.
Just as in the example above, systems often need to express the value of a property in multiple languages. Typically, such systems also try to ensure that developers have a programmatically easy way to navigate the data structures for the language-specific data. In this case, language maps may be utilized.
{ "@context": { ..."occupation": { "@id": "ex:occupation", }"occupation": { "@id": "ex:occupation", "@container": "@language" } }, "name": "Yagyū Muneyoshi", "occupation":{{ "ja": "忍者", "en": "Ninja", "cs": "Nindža" } ... }
The
example
above
expresses
exactly
the
same
information
as
the
previous
example
but
consolidates
all
values
in
a
single
property.
To
access
the
value
in
a
specific
language
in
a
programming
language
supporting
dot-notation
accessors
for
object
properties,
a
developer
may
use
the
property.language
pattern.
For
example,
to
access
the
occupation
in
English,
a
developer
would
use
the
following
code
snippet:
obj.occupation.en
.
Third, it is possible to override the default language by using a value object :
{ "@context": { ... "@language": "ja" }, "name": "花澄","occupation": {"occupation": { "@value": "Scientist", "@language": "en" } }
This
makes
it
possible
to
specify
a
plain
string
by
omitting
the
@language
tag
or
setting
it
to
null
when
expressing
it
using
a
value
object
:
{ "@context": { ... "@language": "ja" },"name": {"name": { "@value": "Frank" }, "occupation": { "@value": "Ninja", "@language": "en" }, "speciality": "手裏剣" }
This section is non-normative.
In
general,
normal
IRI
expansion
rules
apply
anywhere
an
IRI
is
expected
(see
section
5.2
IRIs
).
Within
a
context
definition,
this
can
mean
that
terms
defined
within
the
context
may
also
be
used
within
that
context
as
long
as
there
are
no
circular
dependencies.
For
example,
it
is
common
to
use
the
xsd
namespace
when
defining
typed
value
s:
{ "@context": {,"xsd": "http://www.w3.org/2001/XMLSchema#", "name": "http://xmlns.com/foaf/0.1/name", "age": { "@id": "http://xmlns.com/foaf/0.1/age","@type":"@type": "xsd:integer" }, "homepage": { "@id": "http://xmlns.com/foaf/0.1/homepage", "@type": "@id" } }, ... }
In
this
example,
the
xsd
term
is
defined
and
used
as
a
prefix
for
the
@type
coercion
of
the
age
property.
Terms may also be used when defining the IRI of another term :
{ "@context": {,"foaf": "http://xmlns.com/foaf/0.1/", "xsd": "http://www.w3.org/2001/XMLSchema#","name": ,"name": "foaf:name", "age": {"@id": ,"@id": "foaf:age", "@type": "xsd:integer" }, "homepage": {"@id": ,"@id": "foaf:homepage", "@type": "@id" } }, ... }
Compact IRIs and IRIs may be used on the left-hand side of a term definition.
{ "@context": {,"foaf": "http://xmlns.com/foaf/0.1/", "xsd": "http://www.w3.org/2001/XMLSchema#", "name": "foaf:name","":"foaf:age": { "@type": "xsd:integer" },"": {"foaf:homepage": { "@type": "@id" } }, ... }
In
this
example,
the
compact
IRI
form
is
used
in
two
different
ways.
In
the
first
approach,
foaf:age
declares
both
the
IRI
for
the
term
(using
short-form)
as
well
as
the
@type
associated
with
the
term
.
In
the
second
approach,
only
the
@type
associated
with
the
term
is
specified.
The
full
IRI
for
foaf:homepage
is
determined
by
looking
up
the
foaf
prefix
in
the
context
.
Absolute IRIs may also be used in the key position in a context :
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/", "xsd": "http://www.w3.org/2001/XMLSchema#", "name": "foaf:name", "foaf:age": { "@id": "foaf:age", "@type": "xsd:integer" },"":"http://xmlns.com/foaf/0.1/homepage": { "@type": "@id" } }, ... }
In
order
for
the
absolute
IRI
to
match
above,
the
absolute
IRI
needs
to
be
used
in
the
JSON-LD
document
.
Also
note
that
foaf:homepage
will
not
use
the
{
"@type":
"@id"
}
declaration
because
foaf:homepage
is
not
the
same
as
http://xmlns.com/foaf/0.1/homepage
.
That
is,
terms
are
looked
up
in
a
context
using
direct
string
comparison
before
the
prefix
lookup
mechanism
is
applied.
While
it
is
possible
to
define
a
compact
IRI
,
or
an
absolute
IRI
to
expand
to
some
other
unrelated
IRI
(for
example,
foaf:name
expanding
to
http://example.org/unrelated#species
),
such
usage
is
strongly
discouraged.
The only exception for using terms in the context is that circular definitions are not allowed. That is, a definition of term1 cannot depend on the definition of term2 if term2 also depends on term1 . For example, the following context definition is illegal:
{ "@context": {"term1": "term2:foo","term1": "term2:foo", "term2": "term1:bar" }, ... }
This section is non-normative.
A JSON-LD author can express multiple values in a compact way by using arrays . Since graphs do not describe ordering for links between nodes, arrays in JSON-LD do not provide an ordering of the contained elements by default. This is exactly the opposite from regular JSON arrays, which are ordered by default. For example, consider the following simple document:
{ ... "@id": "http://example.org/people#joebob","nick": ,"nick": [ "joe", "bob", "JB" ], ... }
The example shown above would result in the following data being generated, each relating the node to an individual value, with no inherent order:
Subject | Property | Value |
---|---|---|
http://example.org/people#joebob | http://xmlns.com/foaf/0.1/nick | joe |
http://example.org/people#joebob | http://xmlns.com/foaf/0.1/nick | bob |
http://example.org/people#joebob | http://xmlns.com/foaf/0.1/nick | JB |
Multiple values may also be expressed using the expanded form:
{ "@id": "http://example.org/articles/8","dc:title":"dc:title": [ { "@value": "Das Kapital", "@language": "de" }, { "@value": "Capital", "@language": "en" } ] }
The example shown above would generate the following data, again with no inherent order:
Subject | Property | Value | Language |
---|---|---|---|
http://example.org/articles/8 | http://purl.org/dc/terms/title | Das Kapital | de |
http://example.org/articles/8 | http://purl.org/dc/terms/title | Capital | en |
As
the
notion
of
ordered
collections
is
rather
important
in
data
modeling,
it
is
useful
to
have
specific
language
support.
In
JSON-LD,
a
list
may
be
represented
using
the
@list
keyword
as
follows:
{ ... "@id": "http://example.org/people#joebob", "foaf:nick":{{ "@list": [ "joe", "bob", "jaybee" ] }, ... }
This
describes
the
use
of
this
array
as
being
ordered,
and
order
is
maintained
when
processing
a
document.
If
every
use
of
a
given
multi-valued
property
is
a
list,
this
may
be
abbreviated
by
setting
@container
to
@list
in
the
context
:
{ "@context": { ... "nick": { "@id": "http://xmlns.com/foaf/0.1/nick", "@container": "@list" } }, ... "@id": "http://example.org/people#joebob","nick": ,"nick": [ "joe", "bob", "jaybee" ], ... }
List of lists in the form of list objects are not allowed in this version of JSON-LD. This decision was made due to the extreme amount of added complexity when processing lists of lists.
While
@list
is
used
to
describe
ordered
lists
,
the
@set
keyword
is
used
to
describe
unordered
sets
.
The
use
of
@set
in
the
body
of
a
JSON-LD
document
is
optimized
away
when
processing
the
document,
as
it
is
just
syntactic
sugar.
However,
@set
is
helpful
when
used
within
the
context
of
a
document.
Values
of
terms
associated
with
a
@set
or
@list
container
are
always
represented
in
the
form
of
an
array
,
even
if
there
is
just
a
single
value
that
would
otherwise
be
optimized
to
a
non-array
form
in
compact
form
(see
section
6.18
Compacted
Document
Form
).
This
makes
post-processing
of
JSON-LD
documents
easier
as
the
data
is
always
in
array
form,
even
if
the
array
only
contains
a
single
value.
This section is non-normative.
JSON-LD serializes directed graphs . That means that every property points from a node to another node or value . However, in some cases, it is desirable to serialize in the reverse direction. Consider for example the case where a person and its children should be described in a document. If the used vocabulary does not provide a children property but just a parent property , every node representing a child would have to be expressed with a property pointing to the parent as in the following example.
[ {,"@id": "#homer", "http://example.com/vocab#name": "Homer" }, { "@id": "#bart", "http://example.com/vocab#name": "Bart","http://example.com/vocab#parent": { "@id": "#homer" } }, { "@id": "#lisa", "http://example.com/vocab#name": "Lisa","http://example.com/vocab#parent": { "@id": "#homer" } } ]
Expressing
such
data
is
much
simpler
by
using
JSON-LD's
@reverse
keyword
:
{ "@id": "#homer", "http://example.com/vocab#name": "Homer",: { : ["@reverse": { "http://example.com/vocab#parent": [ { "@id": "#bart", "http://example.com/vocab#name": "Bart" }, { "@id": "#lisa", "http://example.com/vocab#name": "Lisa" } ] } }
The
@reverse
keyword
can
also
be
used
in
expanded
term
definitions
to
create
reverse
properties
as
shown
in
the
following
example:
{ "@context": { "name": "http://example.com/vocab#name","children": { "@reverse": "http://example.com/vocab#parent" } }, "@id": "#homer", "name": "Homer",: ["children": [ { "@id": "#bart", "name": "Bart" }, { "@id": "#lisa", "name": "Lisa" } ] }
This section is non-normative.
At
times,
it
is
necessary
to
make
statements
about
a
graph
itself,
rather
than
just
a
single
node
.
This
can
be
done
by
grouping
a
set
of
nodes
using
the
@graph
keyword
.
A
developer
may
also
name
data
expressed
using
the
@graph
keyword
by
pairing
it
with
an
@id
keyword
as
shown
in
the
following
example:
{ "@context": { "generatedAt": { "@id": "http://www.w3.org/ns/prov#generatedAtTime", "@type": "http://www.w3.org/2001/XMLSchema#date" }, "Person": "http://xmlns.com/foaf/0.1/Person", "name": "http://xmlns.com/foaf/0.1/name", "knows": "http://xmlns.com/foaf/0.1/knows" },"@id": "http://example.org/graphs/73","@id": "http://example.org/graphs/73", "generatedAt": "2012-04-09", "@graph": [ { "@id": "http://manu.sporny.org/about#manu", "@type": "Person", "name": "Manu Sporny", "knows": "http://greggkellogg.net/foaf#me" }, { "@id": "http://greggkellogg.net/foaf#me", "@type": "Person", "name": "Gregg Kellogg", "knows": "http://manu.sporny.org/about#manu" } ] }
The
example
above
expresses
a
named
graph
that
is
identified
by
the
IRI
http://example.org/graphs/73
.
That
graph
is
composed
of
the
statements
about
Manu
and
Gregg.
Metadata
about
the
graph
itself
is
expressed
via
the
generatedAt
property,
which
specifies
when
the
graph
was
generated.
An
alternative
view
of
the
information
above
is
represented
in
table
form
below:
Graph | Subject | Property | Value | Value Type |
---|---|---|---|---|
|
http://example.org/graphs/73 | http://www.w3.org/ns/prov#generatedAtTime | 2012-04-09 | http://www.w3.org/2001/XMLSchema#date |
http://example.org/graphs/73 | http://manu.sporny.org/about#manu | http://www.w3.org/2001/XMLSchema#type | http://xmlns.com/foaf/0.1/Person | |
http://example.org/graphs/73 | http://manu.sporny.org/about#manu | http://xmlns.com/foaf/0.1/name | Manu Sporny | |
http://example.org/graphs/73 | http://manu.sporny.org/about#manu | http://xmlns.com/foaf/0.1/knows | http://greggkellogg.net/foaf#me | |
http://example.org/graphs/73 | http://greggkellogg.net/foaf#me | http://www.w3.org/2001/XMLSchema#type | http://xmlns.com/foaf/0.1/Person | |
http://example.org/graphs/73 | http://greggkellogg.net/foaf#me | http://xmlns.com/foaf/0.1/name | Gregg Kellogg | |
http://example.org/graphs/73 | http://greggkellogg.net/foaf#me | http://xmlns.com/foaf/0.1/knows | http://manu.sporny.org/about#manu |
When
a
JSON-LD
document's
top-level
structure
is
an
object
that
contains
no
other
properties
than
@graph
and
optionally
@context
(properties
that
are
not
mapped
to
an
IRI
or
a
keyword
are
ignored),
@graph
is
considered
to
express
the
otherwise
implicit
default
graph
.
This
mechanism
can
be
useful
when
a
number
of
nodes
exist
at
the
document's
top
level
that
share
the
same
context
,
which
is,
e.g.,
the
case
when
a
document
is
flattened
.
The
@graph
keyword
collects
such
nodes
in
an
array
and
allows
the
use
of
a
shared
context.
{ "@context": ...,"":"@graph": [ { "@id": "http://manu.sporny.org/about#manu", "@type": "foaf:Person", "name": "Manu Sporny", "knows": "http://greggkellogg.net/foaf#me" }, { "@id": "http://greggkellogg.net/foaf#me", "@type": "foaf:Person", "name": "Gregg Kellogg", "knows": "http://manu.sporny.org/about#manu" } ] }
In
this
case,
embedding
doesn't
work
as
each
node
object
references
the
other.
This
is
equivalent
to
using
multiple
node
objects
in
array
and
defining
the
@context
within
each
node
object
:
[ {"@context": ..., "@id": "http://manu.sporny.org/about#manu", "@type": "foaf:Person", "name": "Manu Sporny", "knows": "http://greggkellogg.net/foaf#me" }, {"@context": ..., "@id": "http://greggkellogg.net/foaf#me", "@type": "foaf:Person", "name": "Gregg Kellogg", "knows": "http://manu.sporny.org/about#manu" } ]
This section is non-normative.
At
times,
it
becomes
necessary
to
be
able
to
express
information
without
being
able
to
uniquely
identify
the
node
with
an
IRI
.
This
type
of
node
is
called
a
blank
node
.
JSON-LD
does
not
require
all
nodes
to
be
identified
using
@id
.
However,
some
graph
topologies
may
require
identifiers
to
be
serializable.
Graphs
containing
loops,
e.g.,
cannot
be
serialized
using
embedding
alone,
@id
must
be
used
to
connect
the
nodes.
In
these
situations,
one
can
use
blank
node
identifiers
,
which
look
like
IRIs
using
an
underscore
(
_
)
as
scheme.
This
allows
one
to
reference
the
node
locally
within
the
document,
but
makes
it
impossible
to
reference
the
node
from
an
external
document.
The
blank
node
identifier
is
scoped
to
the
document
in
which
it
is
used.
{ ..."@id": "","@id": "_:n1", "name": "Secret Agent 1", "knows": { "name": "Secret Agent 2","knows": { "@id": "" }"knows": { "@id": "_:n1" } } }
The
example
above
contains
information
about
to
secret
agents
that
cannot
be
identified
with
an
IRI
.
While
expressing
that
agent 1
agent 1
knows
agent 2
agent 2
is
possible
without
using
blank
node
identifiers
,
it
is
necessary
assign
agent 1
agent 1
an
identifier
so
that
it
can
be
referenced
from
agent 2
agent 2
.
It is worth nothing that blank node identifiers may be relabeled during processing. If a developer finds that they refer to the blank node more than once, they should consider naming the node using a dereferenceable IRI so that it can also be referenced from other documents.
This section is non-normative.
Each
of
the
JSON-LD
keywords
,
except
for
@context
,
may
be
aliased
to
application-specific
keywords.
This
feature
allows
legacy
JSON
content
to
be
utilized
by
JSON-LD
by
re-using
JSON
keys
that
already
exist
in
legacy
documents.
This
feature
also
allows
developers
to
design
domain-specific
implementations
using
only
the
JSON-LD
context
.
{ "@context": {, ,"url": "@id", "a": "@type", "name": "http://xmlns.com/foaf/0.1/name" },"": "http://example.com/about#gregg", "": "http://xmlns.com/foaf/0.1/Person","url": "http://example.com/about#gregg", "a": "http://xmlns.com/foaf/0.1/Person", "name": "Gregg Kellogg" }
In
the
example
above,
the
@id
and
@type
keywords
have
been
given
the
aliases
url
and
a
,
respectively.
Since keywords cannot be redefined, they can also not be aliased to other keywords.
This section is non-normative.
Databases are typically used to make access to data more efficient. Developers often extend this sort of functionality into their application data to deliver similar performance gains. Often this data does not have any meaning from a Linked Data standpoint, but is still useful for an application.
JSON-LD
introduces
the
notion
of
index
maps
that
can
be
used
to
structure
data
into
a
form
that
is
more
efficient
to
access.
The
data
indexing
feature
allows
an
author
to
structure
data
using
a
simple
key-value
map
where
the
keys
do
not
map
to
IRIs
.
This
enables
direct
access
to
data
instead
of
having
to
scan
an
array
in
search
of
a
specific
item.
In
JSON-LD
such
data
can
be
specified
by
associating
the
@index
keyword
with
a
@container
declaration
in
the
context:
{ "@context": { "schema": "http://schema.org/", "name": "schema:name", "body": "schema:articleBody", "words": "schema:wordCount", "post": { "@id": "schema:blogPost","@container": "@index" } }, "@id": "http://example.com/", "@type": "schema:Blog", "name": "World Financial News","post": {"post": { "en": { "@id": "http://example.com/posts/1/en", "body": "World commodities were up today with heavy trading of crude oil...", "words": 1539 }, "de": { "@id": "http://example.com/posts/1/de", "body": "Die Werte an Warenbörsen stiegen im Sog eines starken Handels von Rohöl...", "words": 1204 } } }
In
the
example
above,
the
blogPost
post
term
has
been
marked
as
an
index
map
.
The
en
,
de
,
and
ja
keys
will
be
ignored
semantically,
but
preserved
syntactically,
by
the
JSON-LD
Processor.
This
allows
a
developer
to
access
the
German
version
of
the
blogPost
post
using
the
following
code
snippet:
.
obj.blogPost.de
obj.post.de
The interpretation of the data above is expressed in the table below. Note how the index keys do not appear in the Linked Data below, but would continue to exist if the document were compacted or expanded (see section 6.18 Compacted Document Form and section 6.17 Expanded Document Form ) using a JSON-LD processor:
Subject | Property | Value |
---|---|---|
http://example.com/ | http://www.w3.org/1999/02/22-rdf-syntax-ns#type | http://schema.org/Blog |
http://example.com/ | http://schema.org/name | World Financial News |
http://example.com/ | http://schema.org/blogPost | http://example.com/posts/1/en |
http://example.com/ | http://schema.org/blogPost | http://example.com/posts/1/de |
http://example.com/posts/1/en | http://schema.org/articleBody | World commodities were up today with heavy trading of crude oil... |
http://example.com/posts/1/en | http://schema.org/wordCount | 1539 |
http://example.com/posts/1/de | http://schema.org/articleBody | Die Werte an Warenbörsen stiegen im Sog eines starken Handels von Rohöl... |
http://example.com/posts/1/de | http://schema.org/wordCount | 1204 |
This section is non-normative.
The
JSON-LD
Processing
Algorithms
and
API
specification
[
JSON-LD-API
]
defines
a
method
for
expanding
a
JSON-LD
document.
Expansion
is
the
process
of
taking
a
JSON-LD
document
and
applying
a
@context
such
that
all
IRIs,
types,
and
values
are
expanded
so
that
the
@context
is
no
longer
necessary.
For example, assume the following JSON-LD input document:
{ "@context": { "name": "http://xmlns.com/foaf/0.1/name", "homepage": { "@id": "http://xmlns.com/foaf/0.1/homepage", "@type": "@id" } }, "name": "Manu Sporny", "homepage": "http://manu.sporny.org/" }
Running the JSON-LD Expansion algorithm against the JSON-LD input document provided above would result in the following output:
[ { "http://xmlns.com/foaf/0.1/name": [ { "@value": "Manu Sporny" } ], "http://xmlns.com/foaf/0.1/homepage": [ { "@id": "http://manu.sporny.org/" } ] } ]
JSON-LD's
media
type
defines
a
profile
parameter
which
can
be
used
to
signal
or
request
expanded
document
form.
The
profile
URI
identifying
expanded
document
form
is
http://www.w3.org/ns/json-ld#expanded
.
This section is non-normative.
The JSON-LD Processing Algorithms and API specification [ JSON-LD-API ] defines a method for compacting a JSON-LD document. Compaction is the process of applying a developer-supplied context to shorten IRIs to terms or compact IRIs and JSON-LD values expressed in expanded form to simple values such as strings or numbers . Often this makes it simpler to work with document as the data is expressed in application-specific terms. Compacted documents are also typically easier to read for humans.
For example, assume the following JSON-LD input document:
[ { "http://xmlns.com/foaf/0.1/name": [ "Manu Sporny" ], "http://xmlns.com/foaf/0.1/homepage": [ { "@id": "http://manu.sporny.org/" } ] } ]
Additionally, assume the following developer-supplied JSON-LD context:
{ "@context": { "name": "http://xmlns.com/foaf/0.1/name", "homepage": { "@id": "http://xmlns.com/foaf/0.1/homepage", "@type": "@id" } } }
Running the JSON-LD Compaction algorithm given the context supplied above against the JSON-LD input document provided above would result in the following output:
{ "@context": { "name": "http://xmlns.com/foaf/0.1/name", "homepage": { "@id": "http://xmlns.com/foaf/0.1/homepage", "@type": "@id" } }, "name": "Manu Sporny", "homepage": "http://manu.sporny.org/" }
JSON-LD's
media
type
defines
a
profile
parameter
which
can
be
used
to
signal
or
request
compacted
document
form.
The
profile
URI
identifying
compacted
document
form
is
http://www.w3.org/ns/json-ld#compacted
.
This section is non-normative.
The JSON-LD Processing Algorithms and API specification [ JSON-LD-API ] defines a method for flattening a JSON-LD document. Flattening collects all properties of a node in a single JSON object and labels all blank nodes with blank node identifiers . This ensures a shape of the data and consequently may drastically simplify the code required to process JSON-LD in certain applications.
For example, assume the following JSON-LD input document:
{ "@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": [ { "@id": "http://manu.sporny.org/about#manu", "name": "Manu Sporny" }, { "name": "Dave Longley" } ] }
Running the JSON-LD Flattening algorithm against the JSON-LD input document in the example above and using the same context would result in the following output:
{ "@context": { "name": "http://xmlns.com/foaf/0.1/name", "knows": "http://xmlns.com/foaf/0.1/knows" }, "@graph": [ { "@id": "_:b0", "name": "Dave Longley" }, { "@id": "http://manu.sporny.org/about#manu", "name": "Manu Sporny" }, { "@id": "http://me.markus-lanthaler.com/", "name": "Markus Lanthaler", "knows": [ { "@id": "http://manu.sporny.org/about#manu" }, { "@id": "_:b0" } ] } ] }
JSON-LD's
media
type
defines
a
profile
parameter
which
can
be
used
to
signal
or
request
flattened
document
form.
The
profile
URI
identifying
flattened
document
form
is
http://www.w3.org/ns/json-ld#flattened
.
It
can
be
combined
with
the
profile
URI
identifying
expanded
document
form
or
compacted
document
from
.
This section is non-normative.
HTML
script
tags
can
be
used
to
embed
blocks
of
data
in
documents.
This
way,
JSON-LD
content
can
be
easily
embedded
in
HTML
by
placing
it
in
a
script
element
with
the
type
attribute
set
to
application/ld+json
.
<script type="application/ld+json"> { "@context": "http://json-ld.org/contexts/person.jsonld", "@id": "http://dbpedia.org/resource/John_Lennon", "name": "John Lennon", "born": "1940-10-09", "spouse": "http://dbpedia.org/resource/Cynthia_Lennon" }</script></script>
Depending on how the HTML document is served, certain strings may need to be escaped.
Defining how such data may be used is beyond the scope of this specification. The embedded JSON-LD document might be extracted as is or, e.g., be interpreted as RDF.
If JSON-LD content is extracted as RDF [ RDF11-CONCEPTS ], it should be expanded into an RDF Dataset using the Deserialize JSON-LD to RDF Algorithm [ JSON-LD-API ].
JSON-LD is a serialization format for Linked Data based on JSON. It is therefore important to distinguish between the syntax, which is defined by JSON in [ RFC4627 ], and the data model which is an extension of the RDF data model [ RDF11-CONCEPTS ]. The precise details of how JSON-LD relates to the RDF data model are given in section 9. Relationship to RDF .
To ease understanding for developers unfamiliar with the RDF model, the following summary is provided:
_:
.
xsd:string
),
a
number
(
numbers
with
a
non-zero
fractional
part,
i.e.,
the
result
of
a
modulo‑1
operation,
are
interpreted
as
typed
values
with
type
xsd:double
,
all
other
numbers
are
interpreted
as
typed
values
with
type
xsd:integer
),
true
or
false
(which
are
interpreted
as
typed
values
with
type
xsd:boolean
),
or
a
language-tagged
string
.
JSON-LD documents MAY contain data that cannot be represented by the data model defined above. Unless otherwise specified, such data is ignored when a JSON-LD document is being processed. One result of this rule is that properties which are not mapped to an IRI , a blank node , or keyword will be ignored.
Figure 1:
Figure 1:
An
illustration
of
the
data
model.
This appendix restates the syntactic conventions described in the previous sections more formally.
A JSON-LD document MUST be a valid JSON document as described in [ RFC4627 ].
A JSON-LD document MUST be a single node object or an array whose elements are each node objects at the top level.
In contrast to JSON, in JSON-LD the keys in objects MUST be unique.
JSON-LD
allows
keywords
to
be
aliased
(see
section
6.15
Aliasing
Keywords
for
details).
Whenever
a
keyword
is
discussed
in
this
grammar,
the
statements
also
apply
to
an
alias
for
that
keyword
.
For
example,
if
the
active
context
defines
the
term
id
as
an
alias
for
@id
,
that
alias
may
be
legitimately
used
as
a
substitution
for
@id
.
Note
that
keyword
aliases
are
not
expanded
during
context
processing.
A term is a short-hand string that expands to an IRI or a blank node identifier .
A term MUST NOT equal any of the JSON-LD keywords .
To
avoid
forward-compatibility
issues,
a
term
SHOULD
NOT
start
with
an
@
character
as
future
versions
of
JSON-LD
may
introduce
additional
keywords
.
Furthermore,
the
term
MUST
NOT
be
an
empty
string
(
""
)
as
not
all
programming
languages
are
able
to
handle
empty
JSON
keys.
See section 5.1 The Context and section 5.2 IRIs for further discussion on mapping terms to IRIs .
A node object represents zero or more properties of a node in the graph serialized by the JSON-LD document . A JSON object is a node object if it exists outside of a JSON-LD context and:
@value
,
@list
,
or
@set
keywords,
and
@graph
and
@context
.
The properties of a node in a graph may be spread among different node objects within a document. When that happens, the keys of the different node objects need to be merged to create the properties of the resulting node .
A node object MUST be a JSON object . All keys which are not IRIs , compact IRIs , terms valid in the active context , or one of the following keywords MUST be ignored when processed:
@context
,
@id
,
@graph
,
@type
,
@reverse
,
or
@index
If
the
node
object
contains
the
@context
key,
its
value
MUST
be
null
,
an
absolute
IRI
,
a
relative
IRI
,
a
context
definition
,
or
an
array
composed
of
any
of
these.
If
the
node
object
contains
the
@id
key,
its
value
MUST
be
an
absolute
IRI
,
a
relative
IRI
,
or
a
compact
IRI
(including
blank
node
identifiers
).
See
section
5.3
Node
Identifiers
,
section
6.3
Compact
IRIs
,
and
section
6.14
Identifying
Blank
Nodes
for
further
discussion
on
@id
values.
If
the
node
object
contains
the
@graph
key,
its
value
MUST
be
a
node
object
or
an
array
of
zero
or
more
node
objects
.
If
the
node
object
contains
an
@id
keyword,
its
value
is
used
as
the
label
of
a
named
graph.
See
section
6.13
Named
Graphs
for
further
discussion
on
@graph
values.
As
a
special
case,
if
a
JSON
object
contains
no
keys
other
than
@graph
and
@context
,
and
the
JSON
object
is
the
root
of
the
JSON-LD
document,
the
JSON
object
is
not
treated
as
a
node
object
;
this
is
used
as
a
way
of
defining
node
definitions
that
may
not
form
a
connected
graph.
This
allows
a
context
to
be
defined
which
is
shared
by
all
of
the
constituent
node
objects
.
If
the
node
object
contains
the
@type
key,
its
value
MUST
be
either
an
absolute
IRI
,
a
relative
IRI
,
a
compact
IRI
(including
blank
node
identifiers
),
a
term
defined
in
the
active
context
expanding
into
an
absolute
IRI
,
or
an
array
of
any
of
these.
See
section
5.4
Specifying
the
Type
for
further
discussion
on
@type
values.
If
the
node
object
contains
the
@reverse
key,
its
value
MUST
be
a
JSON
object
containing
members
representing
reverse
properties.
Each
value
of
such
a
reverse
property
MUST
be
an
absolute
IRI
,
a
relative
IRI
,
a
compact
IRI
,
a
blank
node
identifier
,
a
node
object
or
an
array
containing
a
combination
of
these.
If
the
node
object
contains
the
@index
key,
its
value
MUST
be
a
string
.
See
section
6.16
Data
Indexing
for
further
discussion
on
@index
values.
Keys in a node object that are not keywords MAY expand to an absolute IRI using the active context . The values associated with keys that expand to an absolute IRI MUST be one of the following:
A value object is used to explicitly associate a type or a language with a value to create a typed value or a language-tagged string .
A
value
object
MUST
be
a
JSON
object
containing
the
@value
key.
It
MAY
also
contain
a
@type
,
a
@language
,
an
@index
,
or
an
@context
key
but
MUST
NOT
contain
both
a
@type
and
a
@language
key
at
the
same
time.
A
value
object
MUST
NOT
contain
any
other
keys
that
expand
to
an
absolute
IRI
or
keyword
.
The
value
associated
with
the
@value
key
MUST
be
either
a
string
,
a
number
,
true
,
false
or
null
.
The
value
associated
with
the
@type
key
MUST
be
a
term
,
a
compact
IRI
,
an
absolute
IRI
,
a
relative
IRI
,
or
null
.
The
value
associated
with
the
@language
key
MUST
have
the
lexical
form
described
in
[
BCP47
],
or
be
null
.
The
value
associated
with
the
@index
key
MUST
be
a
string
.
See section 6.4 Typed Values and section 6.9 String Internationalization for more information on value objects .
A
list
represents
an
ordered
set
of
values.
A
set
represents
an
unordered
set
of
values.
Unless
otherwise
specified,
arrays
are
unordered
in
JSON-LD.
As
such,
the
@set
keyword,
when
used
in
the
body
of
a
JSON-LD
document,
represents
just
syntactic
sugar
which
is
optimized
away
when
processing
the
document.
However,
it
is
very
helpful
when
used
within
the
context
of
a
document.
Values
of
terms
associated
with
a
@set
or
@list
container
will
always
be
represented
in
the
form
of
an
array
when
a
document
is
processed—even
if
there
is
just
a
single
value
that
would
otherwise
be
optimized
to
a
non-array
form
in
compact
document
form
.
This
simplifies
post-processing
of
the
data
as
the
data
is
always
in
a
deterministic
form.
A
list
object
MUST
be
a
JSON
object
that
contains
no
keys
that
expand
to
an
absolute
IRI
or
keyword
other
than
@list
,
@context
,
and
@index
.
A
set
object
MUST
be
a
JSON
object
that
contains
no
keys
that
expand
to
an
absolute
IRI
or
keyword
other
than
@list
,
@context
,
and
@index
.
Please
note
that
the
@index
key
will
be
ignored
when
being
processed.
In
both
cases,
the
value
associated
with
the
keys
@list
and
@set
MUST
be
one
of
the
following
types:
See section 6.11 Sets and Lists for further discussion on sets and lists.
A
language
map
is
used
to
associate
a
language
with
a
value
in
a
way
that
allows
easy
programmatic
access.
A
language
map
may
be
used
as
a
term
value
within
a
node
object
if
the
term
is
defined
with
@container
set
to
@language
.
The
keys
of
a
language
map
MUST
be
strings
representing
[
BCP47
]
language
codes
with
and
the
values
MUST
be
any
of
the
following
types:
See section 6.9 String Internationalization for further discussion on language maps.
An
index
map
allows
keys
that
have
no
semantic
meaning,
but
should
be
preserved
regardless,
to
be
used
in
JSON-LD
documents.
An
index
map
may
be
used
as
a
term
value
within
a
node
object
if
the
term
is
defined
with
@container
set
to
@index
.
The
values
of
the
members
of
an
index
map
MUST
be
one
of
the
following
types:
See section 6.16 Data Indexing for further information on this topic.
A context definition defines a local context in a node object .
A
context
definition
MUST
be
a
JSON
object
whose
keys
MUST
either
be
terms
,
compact
IRIs
,
absolute
IRIs
,
or
the
keywords
@language
,
@base
,
and
@vocab
.
If
the
context
definition
has
a
@language
key,
its
value
MUST
have
the
lexical
form
described
in
[
BCP47
]
or
be
null
.
If
the
context
definition
has
a
@base
key,
its
value
MUST
be
an
absolute
IRI
,
a
relative
IRI
,
or
null
.
If
the
context
definition
has
a
@vocab
key,
its
value
MUST
be
a
absolute
IRI
,
a
compact
IRI
,
a
blank
node
identifier
,
a
term
,
or
null
.
The value of keys that are not keywords MUST be either an absolute IRI , a compact IRI , a term , a blank node identifier , a keyword , null , or an expanded term definition .
An expanded term definition is used to describe the mapping between a term and its expanded identifier, as well as other properties of the value associated with the term when it is used as key in a node object .
An
expanded
term
definition
MUST
be
a
JSON
object
composed
of
zero
or
more
keys
from
@id
,
@reverse
,
@type
,
@language
or
@container
.
An
expanded
term
definition
SHOULD
NOT
contain
any
other
keys.
If
an
expanded
term
definition
has
an
@reverse
member,
it
MUST
NOT
have
an
@id
member
at
the
same
time.
If
an
@container
member
exists,
its
value
MUST
be
null
,
@set
,
or
@index
.
If
the
term
being
defined
is
not
a
compact
IRI
or
absolute
IRI
and
the
active
context
does
not
have
an
@vocab
mapping,
the
expanded
term
definition
MUST
include
the
@id
key.
If
the
expanded
term
definition
contains
the
@id
keyword
,
its
value
MUST
be
null
,
an
absolute
IRI
,
a
blank
node
identifier
,
a
compact
IRI
,
a
term
,
or
a
keyword
.
If
the
expanded
term
definition
contains
the
@type
keyword
,
its
value
MUST
be
an
absolute
IRI
,
a
compact
IRI
,
a
term
,
null
,
or
the
one
of
the
keywords
@id
or
@vocab
.
If
the
expanded
term
definition
contains
the
@language
keyword
,
its
value
MUST
have
the
lexical
form
described
in
[
BCP47
]
or
be
null
.
If
the
expanded
term
definition
contains
the
@container
keyword
,
its
value
MUST
be
either
@list
,
@set
,
@language
,
@index
,
or
be
null
.
If
the
value
is
@language
,
when
the
term
is
used
outside
of
the
@context
,
the
associated
value
MUST
be
a
language
map
.
If
the
value
is
@index
,
when
the
term
is
used
outside
of
the
@context
,
the
associated
value
MUST
be
an
index
map
.
Terms MUST NOT be used in a circular manner. That is, the definition of a term cannot depend on the definition of another term if that other term also depends on the first term.
See section 5.1 The Context for further discussion on contexts.
JSON-LD is a concrete RDF syntax as described in [ RDF11-CONCEPTS ]. Hence, a JSON-LD document is both an RDF document and a JSON document and correspondingly represents an instance of an RDF data model. However, JSON-LD also extends the RDF data model to optionally allow JSON-LD to serialize Generalized RDF Datasets . The JSON-LD extensions to the RDF data model are:
Summarized, these differences mean that JSON-LD is capable of serializing any RDF graph or dataset and most, but not all, JSON-LD documents can be directly interpreted as RDF as described in RDF 1.1 Concepts [ RDF11-CONCEPTS ].
For authors and developers working with blank nodes as properties when deserializing to RDF, three potential approaches are suggested:
The normative algorithms for interpreting JSON-LD as RDF and serializing RDF as JSON-LD are specified in the JSON-LD Processing Algorithms and API specification [ JSON-LD-API ].
Even though JSON-LD serializes generalized RDF Datasets , it can also be used as a RDF graph source . In that case, a consumer MUST only use the default graph and ignore all named graphs. This allows servers to expose data in languages such as Turtle and JSON-LD using content negotiation.
Publishers supporting both dataset and graph syntaxes have to ensure that the primary data is stored in the default graph to enable consumers that do not support datasets to process the information.
This section is non-normative.
The process of serializing RDF as JSON-LD and deserializing JSON-LD to RDF depends on executing the algorithms defined in RDF Serialization-Deserialization Algorithms in the JSON-LD Processing Algorithms and API specification [ JSON-LD-API ]. It is beyond the scope of this document to detail these algorithms any further, but a summary of the necessary operations is provided to illustrate the process.
The procedure to deserialize a JSON-LD document to RDF involves the following steps:
For example, consider the following 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": [ { "@id": "http://manu.sporny.org/about#manu", "name": "Manu Sporny" }, { "name": "Dave Longley" } ] }
Running the JSON-LD Expansion and Flattening algorithms against the JSON-LD input document in the example above would result in the following output:
[ { "@id": "_:b0", "http://xmlns.com/foaf/0.1/name": "Dave Longley" }, { "@id": "http://manu.sporny.org/about#manu", "http://xmlns.com/foaf/0.1/name": "Manu Sporny" }, { "@id": "http://me.markus-lanthaler.com/", "http://xmlns.com/foaf/0.1/name": "Markus Lanthaler", "http://xmlns.com/foaf/0.1/knows": [ { "@id": "http://manu.sporny.org/about#manu" }, { "@id": "_:b0" } ] } ]
Deserializing this to RDF now is a straightforward process of turning each node object into one or more RDF triples. This can be expressed in Turtle as follows:
_:b0 <http://xmlns.com/foaf/0.1/name> "Dave Longley" . <http://manu.sporny.org/about#manu> <http://xmlns.com/foaf/0.1/name> "Manu Sporny" . <http://me.markus-lanthaler.com/> <http://xmlns.com/foaf/0.1/name> "Markus Lanthaler" ;<http://xmlns.com/foaf/0.1/knows> <http://manu.sporny.org/about#manu>, _:b0 .<http://xmlns.com/foaf/0.1/knows> <http://manu.sporny.org/about#manu>, _:b0 .
The process of serializing RDF as JSON-LD can be thought of as the inverse of this last step, creating an expanded JSON-LD document closely matching the triples from RDF, using a single node object for all triples having a common subject, and a single property for those triples also having a common predicate.
This section is non-normative.
The JSON-LD examples below demonstrate how JSON-LD can be used to express semantic data marked up in other linked data formats such as Turtle, RDFa, Microformats, and Microdata. These sections are merely provided as evidence that JSON-LD is very flexible in what it can express across different Linked Data approaches.
This section is non-normative.
The following are examples of transforming RDF expressed in Turtle [ TURTLE ] into JSON-LD.
This section is non-normative.
The
JSON-LD
context
has
direct
equivalents
for
the
Turtle
@prefix
declaration:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . <http://manu.sporny.org/about#manu> a foaf:Person; foaf:name "Manu Sporny";foaf:homepage <http://manu.sporny.org/> .foaf:homepage <http://manu.sporny.org/> .
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/" }, "@id": "http://manu.sporny.org/about#manu", "@type": "foaf:Person", "foaf:name": "Manu Sporny", "foaf:homepage": { "@id": "http://manu.sporny.org/" } }
Both Turtle and JSON-LD allow embedding, although Turtle only allows embedding of blank nodes .
@prefix foaf: <http://xmlns.com/foaf/0.1/> . <http://manu.sporny.org/about#manu> a foaf:Person; foaf:name "Manu Sporny";foaf:knows [ a foaf:Person; foaf:name "Gregg Kellogg" ] .foaf:knows [ a foaf:Person; foaf:name "Gregg Kellogg" ] .
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/" }, "@id": "http://manu.sporny.org/about#manu", "@type": "foaf:Person", "foaf:name": "Manu Sporny", "foaf:knows": { "@type": "foaf:Person", "foaf:name": "Gregg Kellogg" } }
In
JSON-LD
numbers
and
boolean
values
are
native
data
types.
While
Turtle
has
a
shorthand
syntax
to
express
such
values,
RDF's
abstract
syntax
requires
that
numbers
and
boolean
values
are
represented
as
typed
literals.
Thus,
to
allow
full
round-tripping,
the
JSON-LD
Processing
Algorithms
and
API
specification
[
JSON-LD-API
]
defines
conversion
rules
between
JSON-LD's
native
data
types
and
RDF's
counterparts.
Numbers
without
fractions
are
converted
to
xsd:integer
-typed
literals,
numbers
with
fractions
to
xsd:double
-typed
literals
and
the
two
boolean
values
true
and
false
to
a
xsd:boolean
-typed
literal.
All
typed
literals
are
in
canonical
lexical
form.
{ "@context": { "ex": "http://example.com/vocab#" }, "@id": "http://example.com/", "ex:numbers": [ 14, 2.78 ], "ex:booleans": [ true, false ] }
@prefix ex: <http://example.com/vocab#> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . <http://example.com/> ex:numbers "14"^^xsd:integer, "2.78E0"^^xsd:double ;ex:booleans "true"^^xsd:boolean, "false"^^xsd:boolean .ex:booleans "true"^^xsd:boolean, "false"^^xsd:boolean .
Both JSON-LD and Turtle can represent sequential lists of values.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . <http://example.org/people#joebob> a foaf:Person; foaf:name "Joe Bob";foaf:nick ( "joe" "bob" "jaybee" ) .foaf:nick ( "joe" "bob" "jaybee" ) .
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/" }, "@id": "http://example.org/people#joebob", "@type": "foaf:Person", "foaf:name": "Joe Bob", "foaf:nick": { "@list": [ "joe", "bob", "jaybee" ] } }
This section is non-normative.
The following example describes three people with their respective names and homepages in RDFa [ RDFA-CORE ].
<div prefix="foaf: http://xmlns.com/foaf/0.1/"> <ul><li > <a >Bob</a><li typeof="foaf:Person"> <a rel="foaf:homepage" href="http://example.com/bob/" property="foaf:name">Bob</a> </li><li > <a >Eve</a><li typeof="foaf:Person"> <a rel="foaf:homepage" href="http://example.com/eve/" property="foaf:name">Eve</a> </li><li > <a >Manu</a><li typeof="foaf:Person"> <a rel="foaf:homepage" href="http://example.com/manu/" property="foaf:name">Manu</a> </li> </ul> </div>
An example JSON-LD implementation using a single context is described below.
{ "@context": { "foaf": "http://xmlns.com/foaf/0.1/" }, "@graph": [ { "@type": "foaf:Person", "foaf:homepage": "http://example.com/bob/", "foaf:name": "Bob" }, { "@type": "foaf:Person", "foaf:homepage": "http://example.com/eve/", "foaf:name": "Eve" }, { "@type": "foaf:Person", "foaf:homepage": "http://example.com/manu/", "foaf:name": "Manu" } ] }
This section is non-normative.
The following example uses a simple Microformats hCard example to express how Microformats [ MICROFORMATS ] are represented in JSON-LD.
<div class="vcard"> <a class="url fn" href="http://tantek.com/">Tantek Çelik</a> </div>
The
representation
of
the
hCard
expresses
the
Microformat
terms
in
the
context
and
uses
them
directly
for
the
url
and
fn
properties.
Also
note
that
the
Microformat
to
JSON-LD
processor
has
generated
the
proper
URL
type
for
http://tantek.com/
.
{ "@context": { "vcard": "http://microformats.org/profile/hcard#vcard", "url": { "@id": "http://microformats.org/profile/hcard#url", "@type": "@id" }, "fn": "http://microformats.org/profile/hcard#fn" }, "@type": "vcard", "url": "http://tantek.com/", "fn": "Tantek Çelik" }
This section is non-normative.
The HTML Microdata [ MICRODATA ] example below expresses book information as a Microdata Work item.
<dl itemscope itemtype="http://purl.org/vocab/frbr/core#Work" itemid="http://purl.oreilly.com/works/45U8QJGZSQKDH8N"> <dt>Title</dt> <dd><cite itemprop="http://purl.org/dc/terms/title">Just a Geek</cite></dd> <dt>By</dt> <dd><span itemprop="http://purl.org/dc/terms/creator">Wil Wheaton</span></dd> <dt>Format</dt> <dd itemprop="http://purl.org/vocab/frbr/core#realization" itemscope itemtype="http://purl.org/vocab/frbr/core#Expression" itemid="http://purl.oreilly.com/products/9780596007683.BOOK"> <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/BOOK"> Print </dd> <dd itemprop="http://purl.org/vocab/frbr/core#realization" itemscope itemtype="http://purl.org/vocab/frbr/core#Expression" itemid="http://purl.oreilly.com/products/9780596802189.EBOOK"> <link itemprop="http://purl.org/dc/terms/type" href="http://purl.oreilly.com/product-types/EBOOK"> Ebook </dd> </dl>
Note that the JSON-LD representation of the Microdata information stays true to the desires of the Microdata community to avoid contexts and instead refer to items by their full IRI .
[ { "@id": "http://purl.oreilly.com/works/45U8QJGZSQKDH8N", "@type": "http://purl.org/vocab/frbr/core#Work", "http://purl.org/dc/terms/title": "Just a Geek", "http://purl.org/dc/terms/creator": "Whil Wheaton", "http://purl.org/vocab/frbr/core#realization": [ "http://purl.oreilly.com/products/9780596007683.BOOK", "http://purl.oreilly.com/products/9780596802189.EBOOK" ] }, { "@id": "http://purl.oreilly.com/products/9780596007683.BOOK", "@type": "http://purl.org/vocab/frbr/core#Expression", "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/BOOK" }, { "@id": "http://purl.oreilly.com/products/9780596802189.EBOOK", "@type": "http://purl.org/vocab/frbr/core#Expression", "http://purl.org/dc/terms/type": "http://purl.oreilly.com/product-types/EBOOK" } ]
This section has been submitted to the Internet Engineering Steering Group (IESG) for review, approval, and registration with IANA.
profile
A
a
non-empty
list
of
space-separated
URIs
identifying
specific
constraints
or
conventions
that
apply
to
a
JSON-LD
document
according
[
RFC6906
].
A
profile
does
not
change
the
semantics
of
the
resource
representation
when
processed
without
profile
knowledge,
so
that
clients
both
with
and
without
knowledge
of
a
profiled
resource
can
safely
use
the
same
representation.
The
profile
parameter
MAY
be
used
by
clients
to
express
their
preferences
in
the
content
negotiation
process.
If
the
profile
parameter
is
given,
a
server
SHOULD
return
a
document
that
honors
the
profiles
in
the
list
which
are
recognized
by
the
server.
It
is
RECOMMENDED
that
profile
URIs
are
dereferenceable
and
provide
useful
documentation
at
that
URI.
For
more
information
and
background
please
refer
to
[
RFC6906
].
This
specification
defines
three
values
for
the
profile
parameter.
To
request
or
specify
expanded
JSON-LD
document
form
,
the
URI
http://www.w3.org/ns/json-ld#expanded
SHOULD
be
used.
To
request
or
specify
compacted
JSON-LD
document
form
,
the
URI
http://www.w3.org/ns/json-ld#compacted
SHOULD
be
used.
To
request
or
specify
flattened
JSON-LD
document
form
,
the
URI
http://www.w3.org/ns/json-ld#flattened
SHOULD
be
used.
Please
note
that,
according
[
HTTP11
],
the
value
of
the
profile
parameter
has
to
be
enclosed
in
quotes
(
"
)
because
it
contains
special
characters
and,
if
multiple
profiles
are
combined,
whitespace.
When processing the "profile" media type parameter, it is important to note that its value contains one or more URIs and not IRIs. In some cases it might therefore be necessary to convert between IRIs and URIs as specified in section 3 Relationship between IRIs and URIs of [ RFC3987 ].
Since
JSON-LD
is
intended
to
be
a
pure
data
exchange
format
for
directed
graphs,
the
serialization
SHOULD
NOT
be
passed
through
a
code
execution
mechanism
such
as
JavaScript's
eval()
function
to
be
parsed.
An
(invalid)
document
may
contain
code
that,
when
executed,
could
lead
to
unexpected
side
effects
compromising
the
security
of
a
system.
When processing JSON-LD documents, links to remote contexts are typically followed automatically, resulting in the transfer of files without the explicit request of the user for each one. If remote contexts are served by third parties, it may allow them to gather usage patterns or similar information leading to privacy concerns. Specific implementations, such as the API defined in the JSON-LD Processing Algorithms and API specification [ JSON-LD-API ], may provide fine-grained mechanisms to control this behavior.
JSON-LD contexts that are loaded from the Web over non-secure connections, such as HTTP, run the risk of being altered by an attacker such that they may modify the JSON-LD active context in a way that could compromise security. It is advised that any application that depends on a remote context for mission critical purposes vet and cache the remote context before allowing the system to use it.
Given that JSON-LD allows the substitution of long IRIs with short terms, JSON-LD documents may expand considerably when processed and, in the worst case, the resulting data might consume all of the recipient's resources. Applications should treat any data with due skepticism.
Fragment identifiers used with application/ld+json are treated as in RDF syntaxes, as per RDF 1.1 Concepts and Abstract Syntax [ RDF11-CONCEPTS ].
This section is non-normative.
The authors would like to extend a deep appreciation and the most sincere thanks to Mark Birbeck, who contributed foundational concepts to JSON-LD via his work on RDFj. JSON-LD uses a number of core concepts introduced in RDFj, such as the context as a mechanism to provide an environment for interpreting JSON data. Mark had also been very involved in the work on RDFa as well. RDFj built upon that work. JSON-LD exists because of the work and ideas he started nearly a decade ago in 2004.
A large amount of thanks goes out to the JSON-LD Community Group participants who worked through many of the technical issues on the mailing list and the weekly telecons - of special mention are François Daoust, Stéphane Corlosquet, Lin Clark, and Zdenko 'Denny' Vrandečić.
The work of David I. Lehn and Mike Johnson are appreciated for reviewing, and performing several early implementations of the specification. Thanks also to Ian Davis for this work on RDF/JSON.
Thanks to the following individuals, in order of their first name, for their input on the specification: Adrian Walker, Alexandre Passant, Andy Seaborne, Ben Adida, Blaine Cook, Bradley Allen, Brian Peterson, Bryan Thompson, Conal Tuohy, Dan Brickley, Danny Ayers, Daniel Leja, Dave Reynolds, David Booth, David I. Lehn, David Wood, Dean Landolt, Ed Summers, elf Pavlik, Eric Prud'hommeaux, Erik Wilde, Fabian Christ, Jon A. Frost, Gavin Carothers, Glenn McDonald, Guus Schreiber, Henri Bergius, Jose María Alvarez Rodríguez, Ivan Herman, Jack Moffitt, Josh Mandel, KANZAKI Masahide, Kingsley Idehen, Kuno Woudt, Larry Garfield, Mark Baker, Mark MacGillivray, Marko Rodriguez, Marios Meimaris, Matt Wuerstl, Melvin Carvalho, Nathan Rixham, Olivier Grisel, Paolo Ciccarese, Pat Hayes, Patrick Logan, Paul Kuykendall, Pelle Braendgaard, Peter Patel-Schneider, Peter Williams, Pierre-Antoine Champin, Richard Cyganiak, Roy T. Fielding, Sandro Hawke, Simon Grant, Srecko Joksimovic, Stephane Fellah, Steve Harris, Ted Thibodeau Jr., Thomas Steiner, Tim Bray, Tom Morris, Tristan King, Sergio Fernández, Werner Wilms, and William Waites.