RDFa Core 1.1

http://www.w3.org/TR/2010/WD-rdfa-core-20100422 Archived on 2026-04-24 10:37 UTC

RDFa Core 1.1
RDFa Core 1.1
Syntax and processing rules for embedding RDF through attributes
W3C
Working Draft 22 April 2010
This version:
Latest published version:
Latest recommendation:
Editors:
Ben Adida
Creative Commons
Mark Birbeck
webBackplane
Shane McCarron
Applied Testing and Technology, Inc.
Ivan Herman
W3C
This document is also available in these non-normative formats:
PostScript version
and
PDF version
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), All Rights Reserved.
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Abstract
The current Web is primarily made up of an enormous number of documents
that have been created using HTML. These documents contain significant
amounts of structured data, which is largely unavailable to tools and
applications. When publishers can express this data
more completely, and when tools can read it, a new world of user
functionality becomes available, letting users transfer structured
data between applications and web sites, and allowing browsing applications
to improve the user experience: an event on a web page can
be directly imported into a user's desktop calendar; a license on a
document can be detected so that users can be informed of their rights
automatically; a photo's creator, camera setting information,
resolution, location and topic can be published as easily as the original
photo itself, enabling structured search and sharing.
RDFa Core is a specification for attributes to express structured data
in any markup language.
The embedded
data already available in the markup language (e.g., XHTML)
is reused by the RDFa markup, so that
publishers don't need to repeat significant data in the document
content.
The underlying abstract
representation is RDF [
RDF-PRIMER
], which lets publishers build their own
vocabulary, extend others, and evolve their vocabulary with maximal
interoperability over time. The expressed structure is closely tied
to the data, so that rendered data can be copied and pasted along
with its relevant structure.
The rules for interpreting the data are generic, so that there is no
need for different rules for different formats; this allows authors
and publishers of data to define their own formats without having to
update software, register formats via a central authority, or worry
that two formats may interfere with each other.
RDFa shares some of the same goals with microformats [
MICROFORMATS
].
Whereas microformats
specify both a syntax for embedding structured data into HTML
documents and a vocabulary of specific terms for each microformat,
RDFa specifies only a syntax and relies on independent specification
of terms (often called vocabularies or taxonomies) by others. RDFa allows terms
from multiple independently-developed vocabularies to be freely
intermixed and is designed such that the language can be parsed
without knowledge of the specific vocabulary being used.
This document is a detailed syntax specification for RDFa, aimed
at:
those looking to create an RDFa Processor, and who therefore need a
detailed description of the parsing rules;
those looking to recommend the use of RDFa within their
organization, and who would like to create some guidelines for their
users;
anyone familiar with RDF, and who wants to understand more about what
is happening 'under the hood', when an RDFa Processor runs.
For those looking for an introduction to the use of RDFa and some real-world
examples, please consult the
RDFa Primer
How to Read this Document
First, if you are not familiar with either RDFa
or
RDF, and simply
want to add RDFa to your documents, then you may find the RDFa Primer
RDFA-PRIMER
] to be a better introduction.
If you are already familiar with RDFa, and you want to examine the processing
rules — perhaps to create an RDFa Processor — then you'll find the
Processing Model
section of most interest.
It contains an overview of each of the processing steps, followed by more detailed
sections, one for each rule.
If you are not familiar with RDFa, but you
are
familiar with RDF,
then you might find reading the
Syntax Overview
useful,
before looking at the
Processing Model
since it gives a range of examples
of markup that use RDFa. Seeing some examples first should make reading the
processing rules easier.
If you are not familiar with RDF, then you might want to take a look at
the section on
RDF Terminology
before trying to do too much with RDFa. Although RDFa is designed to
be easy to author — and authors don't need to understand RDF to use it —
anyone writing
applications that
consume
RDFa will need to understand RDF. There is a lot
of material about RDF on the web, and a growing range of tools that support RDFa,
this document only contains
enough background on RDF to make the goals of RDFa more clear.
Status of This Document
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 is a revision of RDFa Syntax 1.0 [
RDFA-SYNTAX
].
Once development is complete, if accepted by the
W3C
membership, this document will supersede the
previous
Recommendation
. There are a number of substantive differences between
this version and its predecessor, including:
The removal of the specific rules for XHTML - these are now defined in XHTML+RDFa
XHTML-RDFA
An expansion of the datatypes of some RDFa attributes so that they
can contain Terms, CURIES, or URIs.
The ability to change the default vocabulary when no 'prefix' is specified on a
CURIE.
The ability to reference external RDFa Profile documents; these are used to ease authoring by creating vocabulary term collections.
sample test harness
is available. This set of tests is
not intended to be exhaustive. Users may find the tests to
be useful examples of RDFa usage.
This document was published by the
RDFa Working Group
as a First Public Working Draft. This document is intended to become a
W3C
Recommendation. If you wish to make comments regarding this document, please send them to
public-rdfa-wg@w3.org
archives
). All feedback is welcome.
Publication as a Working Draft 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.
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 also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains
Essential Claim(s)
must disclose the information in accordance with
section 6 of the
W3C
Patent Policy
Table of Contents
1.
Motivation
2.
Syntax Overview
2.1
The RDFa Attributes
2.2
Examples
3.
RDF Terminology
3.1
Statements
3.2
Triples
3.3
URI references
3.4
Plain literals
3.5
Typed literals
3.6
Turtle
3.7
Graphs
3.8
Compact URIs
3.9
Markup Fragments and RDFa
3.10
A description of RDFa in RDF terms
4.
Conformance
4.1
RDFa Processor Conformance
4.2
RDFa Host Language Conformance
5.
Attributes and Syntax
6.
CURIE Syntax Definition
7.
Processing Model
7.1
Overview
7.2
Evaluation Context
7.3
Chaining
7.4
CURIE and URI Processing
7.4.1
Scoping of Prefix Mappings
7.4.2
General Use of CURIEs in Attributes
7.4.3
General Use of Terms in Attributes
7.4.4
Use of CURIEs in Specific Attributes
7.4.5
Referencing Blank Nodes
7.5
Sequence
8.
RDFa Processing in detail
8.1
Changing the evaluation context
8.1.1
Setting the current subject
8.1.1.1
The current document
8.1.1.2
Using
@about
8.1.1.3
Using
@src
8.1.1.4
Creating a new item with
@typeof
8.1.1.5
Determining the subject with neither
@about
nor
@typeof
8.2
Completing 'incomplete triples'
8.3
Object resolution
8.3.1
Literal object resolution
8.3.1.1
Plain Literals
8.3.1.2
Typed literals
8.3.1.3
XML Literals
8.3.2
URI object resolution
8.3.2.1
Using
@resource
to set the object
8.3.2.2
Using
@href
8.3.2.3
Incomplete triples
9.
RDFa Profiles
A.
CURIE Datatypes
A.1
XML Schema Definition
A.2
XML DTD Definition
B.
The RDFa Term Assignment Vocabulary
C.
Change History
D.
Acknowledgments
E.
References
E.1
Normative references
E.2
Informative references
1.
Motivation
This section is non-normative.
RDF/XML [
RDF-SYNTAX
] provides
sufficient flexibility to represent all of the abstract concepts in
RDF [
RDF-CONCEPTS
]. However, it
presents a number of challenges; first it is difficult or impossible to
validate documents that contain RDF/XML using XML Schemas or DTDs,
which therefore makes it difficult to import RDF/XML into other markup
languages. Whilst newer schema languages such as RELAX NG [
RELAXNG-SCHEMA
do provide a way to validate documents
that contain arbitrary RDF/XML, it will be a while before they gain
wide support.
Second, even if one could add RDF/XML directly into an XML
dialect like XHTML, there would be significant data duplication
between the rendered data and the RDF/XML structured data. It would
be far better to add RDF to a document without repeating the
document's existing data. For example, an XHTML document that
explicitly renders its author's name in the text—perhaps as a
byline on a news site—should not need
to repeat this name for the RDF expression of the same concept: it
should be possible to supplement the existing markup in such a way
that it can also be interpreted as RDF.
Another reason for aligning the rendered data with the structured data
is that it is highly beneficial to express the web data's
structure 'in context'; as users often want to transfer structured data from one
application to another, sometimes to or from a non-web-based
application, the user experience can be enhanced.
For example, information about specific
rendered data could be presented to the user via 'right-clicks' on an
item of interest.
In the past, many attributes were 'hard-wired' directly into
the markup language to represent specific concepts. For example, in
XHTML 1.1 [
XHTML11
] and HTML [
HTML401
there is
@cite
; the
attribute allows an author to add information to a document which
is used to indicate the origin of a quote.
However, these 'hard-wired' attributes make it difficult to
define a generic process for extracting metadata from any document
since an RDFa Processor would need to know about each of the special attributes.
One motivation for RDFa has been to devise a means by which documents
can be augmented with metadata in a general, rather than hard-wired, manner.
This has been achieved by creating a fixed set of attributes and parsing rules,
but allowing those attributes to contain properties from any of a number of the
growing range of available RDF vocabularies. In most cases the
values
of those properties
are the information that is already in an author's XHTML document.
RDFa alleviates the
pressure on markup language designers to anticipate all the structural
requirements users of their language might have, by
outlining a new syntax for RDF that
relies only on attributes. By adhering to the concepts and rules in this specification,
language designers can import RDFa into their environment with a minimum of hassle and
be confident that semantic data will be extractable from their documents
by conforming processors.
2.
Syntax Overview
This section is non-normative.
The following examples are intended to help readers who are not familiar with RDFa to
quickly get a sense of how it works.
For a more thorough introduction, please read the RDFa Primer [
RDFA-PRIMER
].
For brevity, in the following examples and throughout this document, assume that the following
vocabulary prefixes have been defined:
biblio:
cc:
dbp:
dbr:
dc:
ex:
foaf:
rdf:
rdfa:
rdfs:
taxo:
xhv:
xsd:
2.1
The RDFa Attributes
RDFa makes use of a number of commonly found attributes, as well as providing a few new ones. Attributes
that already exist in widely deployed languages (e.g., HTML) have the same meaning they
always did, although their syntax has been slightly modified
in some cases.
For example, in (X)HTML,
@rel
already defines the relationship between one document and another. However,
in (X)HTML there is no clear way to add new values; RDFa sets out to explicitly solve this problem, and does so by
allowing URIs as
values. It also introduces the idea of 'compact URIs' — referred to as CURIEs in this
document — which allow a full URI value to be
expressed succinctly. For a complete list of RDFa attribute
names and syntax, see
Attributes and
Syntax
2.2
Examples
As an (X)HTML author you will already be familiar with using
meta
and
link
to add additional information to your documents:

Page 7

...

RDFa makes use of this concept, enhancing it with the ability to make use of other vocabularies
by using compact URIs:
xmlns="http://www.w3.org/1999/xhtml"
prefix="foaf: http://xmlns.com/foaf/0.1/
dc: http://purl.org/dc/elements/1.1/"

My home-page

...

RDFa supports the use of
@rel
and
@rev
on
any element. This is even more useful when with the addition of support for different
vocabularies:
This document is licensed under a
prefix="cc: http://creativecommons.org/ns#"
rel="cc:license"
href="http://creativecommons.org/licenses/by-nc-nd/3.0/">
Creative Commons License
.
Not only can URLs in the document be re-used to provide metadata, but so can inline text:
xmlns="http://www.w3.org/1999/xhtml"
prefix="cal: http://www.w3.org/2002/12/cal/ical#"
Jo's Friends and Family Blog

I'm holding
property="cal:summary"
one last summer Barbecue
,
on September 16th at 4pm.

If some displayed text is different to the actual 'value' it represents,
more precise values can be added, which can optionally include datatypes:
xmlns="http://www.w3.org/1999/xhtml"
prefix="cal: http://www.w3.org/2002/12/cal/ical#
xsd: http://www.w3.org/2001/XMLSchema"
Jo's Friends and Family Blog

I'm holding

one last summer Barbecue
,
on
property="cal:dtstart"
content="2015-09-16T16:00:00-05:00"
datatype="xsd:dateTime"
September 16th at 4pm
.

In many cases a block of markup will contain a number of properties that relate to the same
item; it's possible with RDFa to indicate the type of that item:
xmlns="http://www.w3.org/1999/xhtml"
prefix="cal: http://www.w3.org/2002/12/cal/ical#
xsd: http://www.w3.org/2001/XMLSchema"
Jo's Friends and Family Blog

typeof="cal:Vevent"
I'm holding

one last summer Barbecue
,
on
datatype="xsd:dateTime">
September 16th at 4pm
.

RDFa allows the document to contain metadata information about other documents and resources:
xmlns="http://www.w3.org/1999/xhtml"
prefix="biblio: http://example.org/
dc: http://purl.org/dc/elements/1.1/"

Books by Marco Pierre White

I think White's book
'about="urn:ISBN:0091808189"
typeof="biblio:book"
property="dc:title"
Canteen Cuisine
'
is well worth getting since although it's quite advanced stuff, he
makes it pretty easy to follow. You might also like
about="urn:ISBN:1596913614"
typeof="biblio:book"
property="dc:description"
White's autobiography
.

When dealing with small amounts of markup, it is sometimes easier
to use full URIs,
rather than CURIEs. The previous example can also be written as
follows:

Books by Marco Pierre White

I think White's book
'about="urn:ISBN:0091808189"
typeof="http://example.org/book"
property="http://purl.org/dc/elements/1.1/title"
>Canteen Cuisine'
is well worth getting since although it's quite advanced stuff, he
makes it pretty easy to follow. You might also like
about="urn:ISBN:1596913614"
typeof="http://example.org/book"
property="http://purl.org/dc/elements/1.1/description"
>White's autobiography.

A simple way of defining a portion of a document to use FOAF terms is to use
@vocab
to define a default vocabulary URI:
vocab="http://xmlns.com/foaf/0.1/"
about="#me">
My name is property="name"
>John Doe and my blog is called
rel="homepage"
href="http://example.org/blog/">Understanding Semantics.

the following triples will be generated:
@prefix foaf: .
<#me>
foaf:name
"John Doe" ;
foaf:homepage
.
RDFa also permits external definition of collections of prefixes.
The following RDFa Profile document, residing at
defines
the standard RDF prefixes as well as the Dublin Core vocabulary prefix in RDFa.
prefix="rdfa: http://www.w3.org/ns/rdfa#">

...

This is an example to defining the standard RDF and
Dublin Core prefixes

typeof=""
The "property="rdfa:prefix"
>rdf" prefix can
be used for the URI:
"property="rdfa:uri"
>http://www.w3.org/1999/02/22-rdf-syntax-ns#".

typeof=""
The "property="rdfa:prefix"
>rdfs" prefix can
be used for the URI:
"property="rdfa:uri"
>http://www.w3.org/2000/01/rdf-schema#".

typeof=""
The "property="rdfa:prefix"
>dc" prefix can
be used for the URI:
"property="rdfa:uri"
>http://dublincore.org/documents/dcmi-terms/".

Using
@profile
, the following RDFa snippet:

profile="http://www.example.org/vocab-rdf-dc"
title of the document
and this is a longer comment
on the same document

yields the following triples:
@prefix rdfs: .
@prefix dc: .

dc:title "title of the document" ;
rdfs:comment "and this is a longer comment on the same document" .
It is also possible to define terms. Given the following RDFa Profile document at
prefix="rdfa: http://www.w3.org/ns/rdfa#">

Example RDFa Vocabulary

This is an example RDFa vocabulary that makes it easier to
use the foaf:name and foaf:homepage terms.

typeof=""
The "property="rdfa:term"
>name" term can
be used for the URI:
"property="rdfa:uri"
>http://xmlns.com/foaf/0.1/name".

typeof=""
The "property="rdfa:term"
>homepage" term can
be used for the URI:
"property="rdfa:uri"
>http://xmlns.com/foaf/0.1/homepage".

and the following HTML markup:

My name is property="name"
>John Doe and my blog is called
rel="homepage"
href="http://example.org/blog/">Understanding Semantics.

the following triples will be generated:
@prefix foaf: .
<#me>
foaf:name
"John Doe" ;
foaf:homepage
.
3.
RDF Terminology
This section is non-normative.
The previous section gave examples of typical markup in order to illustrate
the structure of RDFa markup.
However, what RDFa
represents
is RDF. In order to author RDFa you do not need to understand
RDF, although it would certainly help. However, if you are building a system that consumes the RDF
output of a language that supports RDFa you will almost certainly need to understand RDF. This section
introduces the basic concepts and terminology of RDF. For a more thorough explanation of RDF,
please refer to the RDF Concepts document [
RDF-CONCEPTS
and the RDF Syntax Document [
RDF-SYNTAX
].
3.1
Statements
The structured data that RDFa provides access to is a collection of
statements
A statement is a basic unit of information that has been constructed in a specific format to make it easier to
process. In turn, by breaking large sets of information down into a collection of statements, even very complex metadata
can be processed using simple rules.
To illustrate, suppose we have the following set of facts:
Albert was born on March 14, 1879, in Germany. There is a picture of him at
the web address, http://en.wikipedia.org/wiki/Image:Albert_Einstein_Head.jpg.
This would be quite difficult for a machine to interpret, and it is certainly not in a format
that could be passed from one data application to another. However, if we convert the information to a set of statements it begins
to be more manageable. The same information could therefore be
represented by the following shorter 'statements':
Albert was born on March 14, 1879.
Albert was born in Germany.
Albert has a picture at
3.2
Triples
To make this information machine-processable, RDF defines a structure for these statements. A statement
is formally called a
triple
, meaning that it is made up of three components. The first is the
subject
of the
triple, and is what we are making our statements
about
. In all of these examples the subject is 'Albert'.
The second part of a triple is the property of the subject that we want to define. In the examples here, the
properties would be 'was born on', 'was born in', and 'has a picture at'. These are more usually called
predicates
in RDF.
The final part of a triple is called the
object
. In the examples here the three objects have
the values 'March 14, 1879', 'Germany', and 'http://en.wikipedia.org/wiki/Image:Albert_Einstein_Head.jpg'.
3.3
URI references
Breaking complex information into manageable units helps us be specific about our data, but there is still some ambiguity. For example,
which 'Albert' are we talking about? If another system has more facts about 'Albert', how could we know
whether they are about the same person, and so add them to the list of things we know about that person?
If we wanted to find people born in Germany, how could we know that the predicate 'was born in' has the same
purpose as the predicate 'birthplace' that might exist in some other system? RDF solves this problem by replacing our
vague terms with
URI references
URIs are most commonly used to identify web pages, but RDF makes use of them as a way to provide unique identifiers
for concepts. For example, we could identify the subject of all of our statements (the first part of each triple)
by using the DBPedia [
] URI for Albert Einstein, instead of
the ambiguous string 'Albert':

has the name
Albert Einstein.

was born on
March 14, 1879.

was born in
Germany.

has a picture at
URI references are also used to uniquely identify the objects in metadata statements (the third part of each triple). The
picture of Einstein is already a URI, but we could also use a URI to uniquely identify the country Germany. At the same time
we'll indicate that the name and date of birth really are
literals (and not URIs), by putting quotes around them:

has the name
Albert Einstein

was born on
March 14, 1879

was born in

has a picture at
URI references are also used to ensure that predicates are unambiguous; now we can be sure that 'birthplace',
'place of birth', 'Lieu de naissance' and so on, all mean the
same thing:

"Albert Einstein".

"March 14, 1879".

.

.
3.4
Plain literals
Although URI resources are always used for subjects and predicates, the object part of a triple can be either a URI or a
literal
. In the example
triples, Einstein's name is represented by a
plain literal
, which means
that it is a basic string with no type or language
information:

"Albert Einstein"
3.5
Typed literals
Some literals, such as dates and numbers, have very specific meanings, so RDF provides a mechanism for indicating
the type of a literal. A
typed literal
is indicated
by attaching a URI to the end of a
plain literal
, and this URI indicates the literal's datatype. This URI is usually based on
datatypes defined in the
XML Schema Datatypes specification [
XMLSCHEMA-2
]. The following
syntax would be used to
unambiguously express Einstein's date of birth as a literal of
type

"1879-03-14"
^^
3.6
Turtle
RDF itself does not have one set way to express triples, since the key ideas of RDF are the triple and the use of URIs,
and
not
any particular syntax.
However, there are a number of mechanisms for expressing triples, such as RDF/XML [
RDF-SYNTAX-GRAMMAR
], Turtle [
TURTLE
],
and of course RDFa. Many discussions
of RDF make use of the
Turtle
syntax to explain their ideas, since it is quite compact. The examples
we have just seen are already using this syntax, and we'll continue to use it throughout this document when
we need to talk about the RDF that could be generated from some RDFa.
Turtle allows long URIs to be abbreviated by using a URI mapping, which can be used to express a compact URI
as follows:
@prefix dbp: .
@prefix foaf: .

foaf:name
"Albert Einstein" .

dbp:birthPlace
.
Here 'dbp:' has been mapped to the URI for DBPedia and 'foaf:' has been mapped to the URI for the
'Friend of a Friend' taxonomy.
Any URI in Turtle could be abbreviated in this way. This means that we could also have used the same
technique to abbreviate the identifier for Einstein, as well as the datatype indicator:
@prefix dbp: .
@prefix dbr: .
@prefix foaf: .
@prefix xsd: .
dbr:Albert_Einstein
dbp:dateOfBirth "1879-03-14"^^
xsd:date
dbr:Albert_Einstein
foaf:depiction .
When writing examples, you will often see the following URI in the Turtle representation:
<>
This indicates the 'current document', i.e., the document being processed. In reality there would
always be a full URI based on the document's location, but this abbreviation serves to make examples
more compact. Note in particular that the whole technique of abbreviation is merely a way to make
examples more compact, and the actual triples generated would always use the full URIs.
3.7
Graphs
A collection of triples is called a
graph
. All of the triples
that are defined by this specification are contained in the
default graph
by an RDFa Processor.
For more information on graphs and other RDF concepts, see [
RDF-CONCEPTS
].
3.8
Compact URIs
In order to allow for the compact expression of RDF statements,
RDFa allows the contraction of most
URI reference
s into
a form called a 'compact URI', or
CURIE
. A detailed discussion of this
mechanism is in the section
CURIE and URI Processing
Note that CURIEs are only used in the markup and Turtle examples, and will never
appear in the generated
triple
s, which are defined by RDF to use
URI reference
s.
Full details on how CURIEs are processed are in the section titled
CURIE Processing
3.9
Markup Fragments and RDFa
A growing use of embedded metadata is to take fragments of markup and move
them from one document to another. This may happen through the use
of tools, such as
drag-and-drop in a browser, or through snippets of code provided to
authors for inclusion
in their documents. (A good example of the latter is the licensing
fragment provided by Creative Commons.)
However, those involved in creating fragments (either by building
tools, or authoring
snippets), should be aware that this specification does not say how
fragments are processed. Specifically, the processing of a fragment
'outside' of a complete
document is undefined because RDFa processing is largely about context.
Future versions of this or related
specifications may do more to define this behavior.
Developers of tools that process fragments, or authors of fragments
for manual inclusion,
should also bear in mind what will happen to their fragment once it
is included in a complete
document. They should carefully consider the
amount of 'context'
information that will be needed in order to ensure a correct
interpretation of their fragment.
3.10
A description of RDFa in RDF terms
The following is a brief description of RDFa in terms of the RDF terminology introduced
here. It may be
useful to readers with an RDF background:
The aim of RDFa is to allow a single
RDF graph
to be carried in various types
of document markup.
An
RDF graph
comprises
node
s linked by
relationships. The basic unit of an
RDF graph
is a
triple
, in which a
subject
node
is linked to an object
node
via a
predicate
. The
subject
node
is always either a
URI
reference
or a
blank node (or bnode)
the
predicate
is
always
URI reference
, and
the object of a statement can be a
URI reference
, a
literal
, or a
bnode
In RDFa, a subject
URI reference
is generally indicated using
@about
, and predicates are represented using
one of
@property
@rel
, or
@rev
. Objects which are
URI reference
s are
represented using
@href
@resource
or
@src
, whilst objects
that are
literal
s are represented either with
@content
or the content of the
element in question (with an optional datatype expressed using
@datatype
, and an optional language expressed using
a Host Language-defined mechanism such as
@xml:lang
).
4.
Conformance
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.
The key words
must
must not
required
should
should not
recommended
may
, and
optional
in this specification are to be interpreted as described in [
RFC2119
].
4.1
RDFa Processor Conformance
A conforming RDFa Processor
must
make available to a consuming application
a single
RDF graph
containing all possible triples generated by
using the rules in the
Processing Model
section.
This specification uses the term
default graph
to mean all of the triples asserted by a document according to the
Processing Model
section.
A conforming RDFa Processor
may
make available additional triples that have
been generated using rules not described here, but these triples
must not
be made
available in the
default graph
. (Whether these additional triples are made
available in one or more additional
RDF graph
s is implementation-specific, and
therefore not defined here.)
A conforming RDFa Processor
must preserve whitespace in both
plain literal
and
XML literals
. However, it may be the case that
the architecture in which a processor operates does not make all whitespace available. It
is therefore advisable for authors who would like to make their documents consumable across
different processors, to remove any unnecessary whitespace in their markup.
4.2
RDFa Host Language Conformance
Host Languages that incorporate RDFa must adhere to the
following:
All of the
facilities required in this specification
must
be included in the Host
Language.
The attributes defined in this
specification
must
be included in the content model of the Host
Language.
If the Host Language uses XML Namespaces [
XML-NAMES
],
the attributes
in this specification
should
be incorporated in the namespace
of the Host Language.
If the Host Language has its own definition for any
attribute defined in this specification, that definition
must
be such that the processing required by this specification
remains possible when the attribute is used in a way consistent
with the requirements herein.
5.
Attributes and Syntax
This specification defines a number of attributes and the
way in which the values of those attributes are to be
interpreted when generating RDF triples. This section
defines the attributes and the syntax of their values.
about
SafeCURIEorCURIEorURI
, used for stating what the data is about (a 'subject' in RDF terminology);
content
CDATA
string, for supplying machine-readable content for a literal (a 'plain literal object', in RDF terminology);
datatype
TERMorCURIEorURI
representing a datatype, to express the datatype of a literal;
href
(optional)
URI
for
expressing the partner resource of a relationship (a 'resource
object', in RDF terminology);
profile
a whitespace separated list of one or more
URIs
that
reference external definitions of terms and/or prefix mappings. See
RDFa Profiles
prefix
a whitespace separated list of prefix-name URI pairs of the form
NCName
':' ' '+ xs:anyURI
property
a whitespace separated list of
TERMorCURIEorURIs
used for expressing relationships between a subject and some literal text (also a 'predicate');
rel
a whitespace separated list of
TERMorCURIEorURIs
, used for expressing relationships between two resources ('predicates' in RDF terminology);
resource
SafeCURIEorCURIEorURI
for expressing the partner resource of a relationship that is not
intended to be navigable (e.g., a 'clickable' link) (also an 'object');
rev
a whitespace separated list of
TERMorCURIEorURIs
used for expressing reverse relationships between two resources (also 'predicates');
src
(optional)
URI
for expressing the partner resource of a relationship when the resource is
embedded (also a 'resource object');
typeof
a whitespace separated list of
TERMorCURIEorURIs
that indicate the RDF type(s) to associate
with a subject;
vocab
A URI that defines the mapping to
use when a
TERM
is referenced in an attribute value. See
General Use of Terms in Attributes
xmlns:prefix
(optional)
A method of declaring prefix mappings as defined in [
XML-NAMES
].
Prefix mappings declared via this attribute are equivalent to those declared using
@prefix
. If this attribute and
@prefix
declare
a mapping for the same prefix on the same element, the
mapping from
@prefix
must
take precedence. Document authors
should
use
@prefix
, and
should not
mix
@prefix
and this attribute
on the same element.
6.
CURIE Syntax Definition
The key component of RDF is the URI, but these are usually long and unwieldy. RDFa therefore supports a mechanism
by which URIs can be abbreviated, called 'compact URIs' or simply, CURIEs.
A CURIE is comprised of two components, a
prefix
and a
reference
. The prefix is separated from the reference by a colon
). In general use it is possible to omit the prefix, and so create a CURIE that makes use of the
'default prefix' mapping; in RDFa the 'default prefix' mapping is
It's also possible to omit both the prefix
and
the colon, and so create a CURIE that contains
just a reference which makes use of the 'no prefix' mapping. This specification
does not define a default 'no prefix' mapping. However, Host Languages
may
define a default. This mapping
may
be changed via
@vocab
The working group has not reached consensus on whether there should be a default prefix
mapping defined in RDFa Core, or whether it should be defined in Host Languages.
The general syntax of a CURIE can be summarised as follows:
prefix
:=
NCName
reference
:= irelative-ref (as defined in [
RFC3987
])
curie := [ [ prefix ] ':' ] reference
safe_curie := '[' [ [ prefix ] ':' ] reference ']'
The production
safe_curie
is not required, even in situations
where an attribute value is permitted to be a CURIE or a URI:
A URI that uses a scheme that is not an in-scope
mapping
cannot
be confused with a CURIE. The concept of a
safe_curie is retained for backward compatibility.
In normal evaluation of CURIEs the following context information would need to be provided:
a set of mappings from prefixes to URIs;
a mapping to use with the default prefix (for example,
:p
);
a mapping to use when there is no prefix (for example,
);
a mapping to use with the '_' prefix, which is used to generate unique identifiers (for example,
_:p
).
In RDFa these values are defined as follows:
the
set of mappings from prefixes to URIs
is provided by the current in-scope prefix declarations of the
current element
during parsing;
the
mapping to use with the default prefix
is the current default prefix mapping;
the
mapping to use when there is no prefix
is not defined, which effectively prohibits the use of CURIEs that do not contain a colon (however, see
General Use of Terms in Attributes
) ;
the
mapping to use with the '_' prefix
, is not explicitly stated, but since it is used to generate
bnode
s,
its implementation needs to be compatible with the RDF definition and rules in
Referencing Blank Nodes
A document
should not
define a mapping for the '_' prefix. A Conforming RDFa Processor
must
ignore any definition of a mapping for the '_' prefix.
A CURIE is a representation of a full URI. The rules for determining that URI are:
If a CURIE consists of an empty
prefix
and a
reference
the URI is obtained by taking the current default prefix mapping and concatenating
it with the
reference
. If there is no current default prefix
mapping, then this is not a valid CURIE and
must
be ignored.
Otherwise, if a CURIE consists of a non-empty
prefix
and
reference
and if there is an in-scope mapping for
prefix
, then the URI is created
by using that mapping, and concatenating it with the
reference
Finally, if there is no in-scope mapping for
prefix
, then the value is not a CURIE.
Note that the resulting URI
must
be a syntactically valid IRI [
RFC3987
]. For a more detailed explanation see
CURIE and URI Processing
Note that while the
lexical space
of a CURIE is as defined in
curie
above,
the
value space
is the set of IRIs.
7.
Processing Model
This section looks at a generic set of processing rules for creating a set of triples that represent the
structured data present in an RDFa document. Processing need not follow the DOM traversal technique outlined
here, although the effect of following some other manner of processing must be the same as if the processing
outlined here were followed. The processing model is explained using the idea of DOM traversal
which makes it easier to describe (particularly in relation to the
evaluation context
).
Note that in this section, explanations about
the processing model or guidance to implementors are enclosed
in sections like this.
7.1
Overview
Evaluating a document for RDFa triples is carried out by starting at the document object, and then
visiting each of its child elements in turn, in document order, applying processing rules. Processing
is recursive in that for each child element the processor also visits each of
its
child elements,
and applies the same processing rules.
In some environments there will be little difference between starting at the root element of
the document, and starting at the document object itself. It is defined this way because in some
environments important information is present at the document object level which is not present on the
root element.
As processing continues, rules are applied which may generate triples, and may also change the
evaluation context
information that will then be used when processing descendant elements.
This specification does not say anything about what should happen to the triples generated, or whether more
triples might be generated during processing than are outlined here. However, to be conforming, an
RDFa processor
must
act as if at a minimum the rules in this section are applied, and a single
RDF graph
produced. As described in the
RDFa Processor Conformance
section,
any additional triples generated
must not
appear in the
default graph
7.2
Evaluation Context
During processing, each rule is applied using information provided by an
evaluation context
An initial context is created when processing begins. That context has the following members:
The
base
. This will usually be the URL of the document being processed, but it could be some other URL,
set by some other mechanism, such as the (X)HTML
base
element. The important thing is that it
establishes a URL against which relative paths can be resolved.
The
parent subject
. The initial value will be the same as the initial value of
base
, but
it will usually change during the course of processing.
The
parent object
. In some situations the object of a statement becomes the subject of any
nested statements, and this property is used to convey this value. Note that this value may be a
bnode
, since in some
situations a number of nested statements are grouped
together on one
bnode
This means that the
bnode
must be set in the containing statement and passed down, and this property is
used to convey this value.
A list of current, in-scope
URI mappings
A list of
incomplete triple
s. A triple can be incomplete when no object resource is provided alongside
a predicate that requires a resource (i.e.,
@rel
or
@rev
). The triples can be completed
when a resource becomes available, which will be when the next subject is specified (part of the process called
chaining
).
The
language
. Note that there is no default language.
The
term mappings
, a list of terms and their associated
URIs. This specification does not define an initial list. Host Languages
may
define
an initial list. If a Host Language provides an initial list, it
should
do so via
an RDFa Profile document.
The
default vocabulary
, a value to
use as the prefix URI when a
term
is used. This
specification does not define an initial setting for the default
vocabulary. Host Languages
may
define an initial setting.
During the course of processing, new
evaluation context
s are created
which are passed to each child element.
The rules described below will determine the values of the items in the context. Additionally, some rules will cause new
triples to be created by combining information provided by an element
with information from the
evaluation context
During the course of processing a number of locally scoped values are needed, as follows:
An initially empty list of
URI mapping
s, called the
local list of URI mappings
An initially empty
list of incomplete triples
, called the
local list of incomplete triples
An initially empty
language
value.
recurse
flag. Processing generally continues recursively through the entire tree of elements available. However,
if an author indicates that some branch of the tree should be treated as an XML literal, no further processing should
take place on that branch, and setting this flag to
false
would have that effect.
skip element
flag, which indicates whether the
current element
can safely be ignored since it has
no relevant RDFa attributes. Note that descendant elements will still be processed.
new subject
value, which once calculated will set the
parent subject
property in an
evaluation context
as well as being used to complete any
incomplete triple
s, as described in the next section.
A value for the
current object literal
, the literal to use when creating triples that have a literal object.
A value for the
current object resource
, the resource to use when creating triples that have a resource object.
The
local term mappings
, a list of terms and their associated
URIs.
local default vocabulary
, a URI to use as a prefix mapping when a
term
is used.
7.3
Chaining
Statement
chaining
is an RDFa feature that allows the author to link RDF statements together while avoiding unnecessary repetitive markup.
For example, if an author were to add statements as children of an object that was a resource, these statements
should be interpreted as being about that resource:

Albert Einstein
1879-03-14

resource="http://dbpedia.org/resource/Germany"
Federal Republic of Germany

In this example we can see that an object resource ('Germany'), has become the subject for nested statements. This markup
also illustrates the basic chaining pattern of 'A has a B has a C' (i.e., Einstein has a birth place of Germany, which has
a long name of "Federal Republic of Germany").
It's also possible
for the subject of nested statements to provide the object for
containing
statements — essentially the reverse
of the example we have just seen. To illustrate, we'll take an example of the type of chaining just described,
and show how it could be marked up more efficiently. To start, we mark up
the fact that Albert Einstein had both German and American citizenship:

Now, we show the same information, but this time we create an
incomplete triple
from the citizenship part,
and then use any number of further subjects to 'complete' that triple, as follows:

In this example, the
incomplete triple
actually gets completed twice, once for Germany and once for the USA,
giving exactly the same information as we had in the earlier example:

dbp:citizenship .

dbp:citizenship .
Chaining can sometimes involve elements containing relatively minimal markup, for example showing only one resource, or only one predicate.
Here the
img
element is used to carry a picture of Einstein:

rel="foaf:depiction"

When such minimal markup is used, any of the resource-related attributes could act as a subject or an object in the chaining:
about="http://dbpedia.org/resource/Albert_Einstein"
rel="dbp:citizenship"
about="http://dbpedia.org/resource/Germany"
>
about="http://dbpedia.org/resource/United_States"
>

7.4
CURIE and URI Processing
Since RDFa is ultimately a means for transporting RDF, a key concept is the
resource
and its manifestation as a
URI. RDF deals with complete URIs (not relative paths); when converting RDFa to triples, any relative URIs
must
be
resolved relative to the base URI, using the algorithm defined in section 5 of RFC 3986 [
URI
],
Reference Resolution
The values of
RDFa attributes
that refer to URIs
use three different datatypes:
URI
SafeCURIEorCURIEorURI
or
TERMorCURIEorURI
. All these attributes are mapped,
after processing, to URIs. The handling of these attributes is as follows:
URI
The content is a URI, and is used as such.
SafeCURIEorCURIEorURI
When the value is surrounded by square brackets, then the content within
the brackets is evaluated as a CURIE according to the
CURIE Syntax definition
If it is not a valid CURIE, the value
must
be ignored.
Otherwise, the value is evaluated as a CURIE. If it is a valid CURIE, the resulting URI is used; otherwise, the value is processed as a URI.
TERMorCURIEorURI
If the value is an
NCName
then it is evaluated as a term according to
General Use of Terms in Attributes
. Note that this step may mean that the value is to be ignored.
Otherwise, the value is evaluated as a CURIE. If it is a valid CURIE, the resulting URI is used; otherwise, the value will be processed as a URI.
For example, the full URI for Albert Einstein on DPPedia is:
This can be shortened by authors to make the information easier to manage, using a CURIE. The first step is for the
author to create a prefix mapping that links a prefix to some leading segment of the URI. In RDFa these mappings are
expressed using the XML namespace syntax:
prefix="db: http://dbpedia.org/"
...

Once the prefix has been established, an author can then use it to shorten a URI as follows:

...

The author is free to split the URI at any point, as long as it begins at the left end. However, since a common
use of CURIEs is to make available libraries of terms and values, the prefix will usually be mapped to some
common segment that provides the most re-use, often provided by those who manage the library of terms. For example,
since DBPedia contains an enormous list of resources, it is more efficient to create a prefix mapping that uses the
base location of the resources:
prefix="dbr: http://dbpedia.org/resource/"

...

Note that it is generally considered a bad idea to use relative paths in prefix declarations. Since it is possible
that an author may ignore this guidance, it is further possible that the URI obtained from a CURIE is relative. However, since
all URIs must be resolved relative to
base
before being used to create triples, the use of relative paths should
not have any effect on processing.
7.4.1
Scoping of Prefix Mappings
CURIE prefix mappings are defined on the current element and
its descendants.
For example, the URIs expressed by the following two CURIEs are
different, despite the common prefix, because the prefix mappings are locally scoped:
prefix="dbr: http://dbpedia.org/resource/"

...

prefix="dbr: http://someotherdb.org/resource/"

...

7.4.2
General Use of CURIEs in Attributes
There are a number of ways that attributes make use of CURIEs, and they need to be dealt with
differently. These are:
An attribute may allow one or more values that are a mixture of CURIEs and URIs. In this case any value that is not
a CURIE, as outlined in section
CURIE Syntax Definition
will be processed as a URI.
If the value
is
surrounded by square
brackets, then the content within the brackets is always evaluated according to the rules in
CURIE Syntax Definition
- and if that content is not a CURIE, then the content
must
be ignored.
An empty attribute value (e.g.,
typeof=''
is
still
a CURIE, and is processed as such. The rules for
this processing are defined in
Sequence
Specifically, however, an empty attribute value is
never
treated
as a relative URI by this specification.
An example of an attribute that can contain a CURIEorURI is
@about
. To express a URI directly, an author might do
this:
about="http://dbpedia.org/resource/Albert_Einstein"
...

whilst to express the URL above as a CURIE they would do this:
about="dbr:Albert_Einstein"
...

The author could also use a safe CURIE, as follows:
about="[dbr:Albert_Einstein]"
...

Since non-CURIE values
must
be ignored, the following value in
@about
would
not
set a new subject, since
@about
does not permit the
use of
TERM
s, and the CURIE has no prefix separator.
about="[Albert_Einstein]"
...

However, this markup
would
set a subject, since it is not a CURIE, but a valid relative URI:
about="Albert_Einstein"
...

Note that several RDFa attributes are able to also take
as their value.
This is discussed in the next section.
7.4.3
General Use of Terms in Attributes
Some RDFa attributes have a datatype that permits a term to be referenced.
RDFa defines the syntax of a term as:
term :=
NCName
When an RDFa attribute permits the use of a term, and the value
being evaluated matches the production for term above, it is
transformed to a URI using the following logic:
If the
term
is in the
local term mappings
, use
the associated URI.
Otherwise, if there is a
local default vocabulary
the URI is obtained by concatenating that
value and the
term
Finally, if there is no
local default vocabulary
the
term
has no associated URI and
must
be ignored.
One ramification of these rules is that, if an attribute
has the datatype
TERMorCURIEorURI
, and the value matches
the production for term but there is no
local default vocabulary
then the term is ignored.
7.4.4
Use of CURIEs in Specific Attributes
The general rules discussed in the previous sections apply to the RDFa attributes in the following ways:
@about
and
@resource
support either a
SafeCURIE, a CURIE, or a URI.
@href
and
@src
are as defined
in the Host Language (e.g., XHTML), and support only a URI.
@profile
and
@vocab
also only support a URI.
@property
@datatype
@typeof
@rel
, and
@rev
support Terms, CURIEs, or URIs.
Any value that matches a defined term
must
be expanded
into a reference to the corresponding URI. For example
in [
XHTML-RDFA
] the following examples:

would each generate the following triple:
<> .
7.4.5
Referencing Blank Nodes
In RDFa, it is possible to establish
relationships using various types of
resource references, including
bnode
s.
If a subject or object is defined using a CURIE, and that CURIE explicitly
names a
bnode
, then
a Conforming Processor
must
create the
bnode
when it is encountered
during parsing.
The RDFa Processor
must
also ensure
that no
bnode
created automatically (as a result of
chaining
has a name that
collides with a
bnode
that is defined by explicit reference in a CURIE.
Consider the following example:
about="_:john"
rel="foaf:mbox"
href="mailto:john@example.org" />
about="_:sue"
rel="foaf:mbox"
href="mailto:sue@example.org" />
about="_:john"
rel="foaf:knows"
resource="_:sue" />
In the above fragment, two
bnodes
are explicitly created as the subject
of triples. Those
bnodes
are then referenced to demonstrate the
relationship between the parties. After processing, the following
triples will be generated:
_:john foaf:mbox .
_:sue foaf:mbox .
_:john foaf:knows _:sue .
7.5
Sequence
Processing would normally begin after the document to be parsed has been completely loaded. However, there is no
requirement for this to be the case, and it is certainly possible to use a stream-based approach, such as
SAX [
SAX
] to extract
the RDFa information. However, if some approach other than the DOM traversal technique defined here is used, it
is important to ensure that Host Language-specific processing rules are applied
(e.g., XHTML+RDFa [
XHTML-RDFA
] indicates the
base
element can be used, and
base
will affect the interpretation of URIs in
meta
or
link
elements even if those elements are before the
base
element in the stream).
At the beginning of processing, an initial
evaluation context
is created, as follows:
the
base
is set to the URL of the document (or another value specified in a language specific manner such as the HTML
base
element);
the
parent subject
is set to the
base
value;
the
parent object
is set to null;
the
list of URI mappings
is empty;
the
list of incomplete triples
is empty;
the
language
is set to null.
the
term mappings
is set to null (or a Host Language
defined list).
the
default vocabulary
is set to null (or a Host Language
defined value).
Processing begins by applying the processing rules below to the document object, in the context of this initial
evaluation context
. All elements in the tree are also processed according to the rules described
below, depth-first, although the
evaluation context
used for each set of rules will be based on
previous rules that may have been applied.
This specification assumes that certain
elements are present in the Host Language (e.g.,
head
). If these elements are not supported in
the Host Language, then the corresponding processing rules
are not relevant for that language.
The working group as not reached consensus as to whether to include
the optional attributes in this specification, or whether to have them defined in the
relevant Host Language specifications.
The processing rules are:
First, the local values are initialized, as follows:
the
recurse
flag is set to 'true';
the
skip element
flag is set to 'false';
new subject
is set to null;
current object resource
is set to null;
the
local list of URI mappings
is set to the list of URI mappings from the
evaluation context
the
local list of incomplete triples
is set to null;
the
current language
value is set to the
language
value from the
evaluation context
the
local term mappings
is set to the
term mappings
from the
evaluation context
the
local default vocabulary
is set to the
default vocabulary
from the
evaluation context
Note that some of the local variables are temporary containers for values that will be passed to descendant elements via an
evaluation context
. In some cases the containers will have the same name, so to make it clear which is being acted upon
in the following steps, the local version of an item will generally be referred to as such.
First the
current element
is examined for any change to the
default vocabulary
via
@vocab
. If
@vocab
is present and contains a value, its value updates the
local default vocabulary
. If
the value is empty, then the
local default vocabulary
must
be reset
to the Host Language defined default.
A Host Language is not required to define a default vocabulary.
In such a case, setting
@vocab
to the empty value has the effect
of clearing the
local default vocabulary
Next the
current element
is parsed for any updates to the
local term mappings
and
local list of URI mappings
via
@profile
. If
@profile
is present, its value is processed as defined in
RDFa Profiles
Any new terms or URI mappings are merged into respective local lists. They
are in effect for this element and for its children.
Next, the
current element
is then examined for
URI mapping
s and these are added to the
local list of URI mappings
. Note that a
URI mapping
will simply
overwrite any current mapping in the list that has the same name;
Mappings are defined via
@prefix
For backward compatibility, some Host Languages
may
also permit the
definition of mappings via
@xmlns
. In this case, the value to be mapped is
set by the XML namespace
prefix, and the value to map is the value of the attribute — a URI.
Regardless of how the mapping is declared,
the value to be mapped
must
be converted to lower case,
and the URI is not processed in any way; in
particular if it is a relative path it is not resolved
against the current
base
. Authors
should not
use relative paths as the URI.
The
current element
is also parsed for any language information, and if present,
current language
is set accordingly;
Host Languages that incorporate RDFa
may
provide a
mechanism for specifying the natural language of
an element and its contents (e.g., XML provides
the general-purpose XML attribute
@xml:lang
).
If the
current element
contains no
@rel
or
@rev
attribute, then the next step is to
establish a value for
new subject
. Any of the attributes that can carry a resource can set
new subject
new subject
is set to the URI obtained from the first match from the following rules:
by using the URI from
@about
, if present, obtained according to the section on
CURIE and URI Processing
otherwise
, by using the URI from
@src
, if present, obtained according to the section on
CURIE and URI Processing
otherwise
, by using the URI from
@resource
, if present, obtained according to the section on
CURIE and URI Processing
otherwise
, by using the URI from
@href
, if present, obtained according to the section on
CURIE and URI Processing
If no URI is provided by a resource attribute, then the
first match from the following rules will apply:
if
@typeof
is present,
then
new subject
is set to be
a newly created
bnode
otherwise
, if
parent object
is present,
new subject
is set to the value of
parent object
. Additionally, if
@property
is
not
present then
the
skip element
flag is set to 'true';
If the
current element
does
contain a
@rel
or
@rev
attribute, then the next step
is to establish
both
a value for
new subject
and a value for
current object resource
new subject
is set to the URI obtained from the first match from the following rules:
by using the URI from
@about
, if present, obtained according to the section on
CURIE and URI Processing
otherwise
, by using the URI from
@src
, if present, obtained according to the section on
CURIE and URI Processing
If no URI is provided then the first match from the
following rules will apply:
if
@typeof
is present,
then
new subject
is set to be
a newly created
bnode
otherwise
, if
parent object
is present,
new subject
is set to that.
Then the
current object resource
is set to the URI obtained from the first match from the
following rules:
by using the URI from
@resource
, if present, obtained according to the section on
CURIE and URI Processing
otherwise
, by using the URI from
@href
, if present, obtained according to the section on
CURIE and URI Processing
Note that final value of the
current object resource
will either be null (from initialization) or a full URI.
If in any of the previous steps a
new subject
was set to a non-null value, it is now used to provide a subject
for type values;
One or more 'types' for the
new subject
can be set by using
@typeof
. If present,
the attribute must contain one or more URIs, obtained according to the section on
URI and CURIE Processing
, each of which is used to generate a triple as follows:
subject
new subject
predicate
object
full URI of 'type'
Note that none of this block is executed if there is no
new subject
value, i.e.,
new subject
remains null.
If in any of the previous steps a
current object resource
was set to a non-null value, it is now used to
generate triples:
Predicates for the
current object resource
can be set by using one or both of the
@rel
and
@rev
attributes:
If present,
@rel
may contain one or more URIs, obtained
according to the section on
CURIE and URI Processing
each of which is
used to generate a triple as follows:
subject
new subject
predicate
full URI
object
current object resource
If present,
@rev
may contain one or more URIs, obtained according to the section on
CURIE and URI Processing
each of which is used to generate a triple
as follows:
subject
current object resource
predicate
full URI
object
new subject
If however
current object resource
was set to null, but there are predicates present,
then they must be stored as
incomplete triple
s, pending the discovery of a subject that
can be used as the object. Also,
current object resource
should be set to a newly created
bnode
Predicates for
incomplete triple
s can be set by using one or both of the
@rel
and
@rev
attributes:
If present,
@rel
must contain one or more URIs, obtained
according to the section on
CURIE and URI Processing
each
of which is added to the
local list of incomplete triples
as follows:
predicate
full URI
direction
forward
If present,
@rev
must contain one or more URIs, obtained according to the section on
CURIE and URI Processing
, each of which is added to the
local list of incomplete triples
as follows:
predicate
full URI
direction
reverse
The next step of the iteration is to establish any
current object literal
Predicates for the
current object literal
can be set by using
@property
. If present, one or more URIs
are obtained according to the section on
CURIE and URI Processing
, and then the actual
literal value is obtained as follows:
as a
typed literal
if:
@datatype
is present, and does not have an empty value, and is not set
to
rdf:XMLLiteral
The actual literal is either the value of
@content
(if present)
or
a string created by concatenating
the value of all descendant text nodes, of the
current element
in turn. The final string includes
the datatype URI, as described in [
RDF-CONCEPTS
], which will have been obtained according to the section on
CURIE and URI Processing
as a
plain literal
if:
@content
is present;
or
all children of the
current element
are text nodes;
or
there are no child nodes (in which case the literal value is the empty string);
or
the body of the
current element
does
have non-text child nodes
but
@datatype
is present, with an empty value.
Additionally, if there is a value for
current language
then the value of the
plain literal
should
include this language information, as described in [
RDF-CONCEPTS
]. The actual literal is either the value of
@content
(if present)
or
a string created by concatenating the text content of each of the descendant elements of the
current element
in document order.
as an
XML literal
if:
the
current element
has any child nodes that are not simply text nodes, and
@datatype
is
not present, or is present, but is set to
rdf:XMLLiteral
The value of the
XML literal
is a string created by serializing to text, all nodes that are
descendants of the
current element
, i.e., not including the element itself, and giving it a datatype of
rdf:XMLLiteral
. The format of the
resulting serialized content is as defined in
Exclusive XML Canonicalization Version
XML-EXC-C14N
].
The
current object literal
is then used with each predicate to generate a triple as follows:
subject
new subject
predicate
full URI
object
current object literal
Once the triple has been created, if the
datatype
of the
current object literal
is
rdf:XMLLiteral
then the
recurse
flag is set to
false
If the
skip element
flag is 'false',
and
new subject
was set to a non-null value, then any
incomplete triple
within the current context
should be completed:
The
list of incomplete triples
from the current
evaluation context
not
the
local list of incomplete triples
) will contain zero or more predicate URIs. This list is
iterated, and each of the predicates is used with
parent subject
and
new subject
to generate
a triple. Note that at each level there are
two
lists of
incomplete triple
s; one for the current processing level (which is passed to each child element in the previous
step), and one that was received as part of the
evaluation context
. It is the latter that is used in processing
during this step.
Note that each
incomplete triple
has a
direction
value that it used to determine what
will become the subject, and what will become the object, of each generated triple:
If
direction
is 'forward'
then the following triple is generated:
subject
parent subject
predicate
the predicate from the iterated
incomplete triple
object
new subject
If
direction
is not 'forward' then this is the triple generated:
subject
new subject
predicate
the predicate from the iterated
incomplete triple
object
parent subject
If the
recurse
flag is 'true', all elements that are children of the
current element
are processed using the rules
described here, using a new
evaluation context
, initialized as follows:
If the
skip element
flag is 'true' then the new
evaluation context
is a copy of the current context
that was passed in to this level of processing, with the
language
and
list of URI mappings
values
replaced with the local values;
Otherwise, the values are:
the
base
is set to the
base
value of the current
evaluation context
the
parent subject
is set to the value of
new subject
, if non-null,
or
the
value of the
parent subject
of the current
evaluation context
the
parent object
is set to value of
current object resource
, if non-null,
or
the value of
new subject
, if non-null,
or
the value of the
parent subject
of the current
evaluation context
the
list of URI mappings
is set to the
local list of URI mappings
the
list of incomplete triples
is set to the
local list of incomplete triples
language
is set to the value of
current language
the
term mappings
is set to the value of the
local term mappings
the
default vocabulary
is set to the value of the
local default vocabulary
8.
RDFa Processing in detail
This section provides an in-depth examination of the processing steps described in the previous section. It also includes
examples which may help clarify some of the steps involved.
The key to processing is that a triple is generated whenever a predicate/object combination is detected. The actual triple
generated
will include a subject that may have been set previously, so this is
tracked in the current
evaluation context
and is called
the
parent subject
. Since the subject will default to the current document if it hasn't been set explicitly, then
a predicate/object combination is always enough to generate one or more triples.
The attributes for setting a predicate are
@rel
@rev
and
@property
, whilst the attributes
for setting an object are
@resource
@href
@content
, and
@src
@typeof
is unique in that it sets
both
a predicate and an object at the same time (and also a subject when it appears in the absence of other attributes that would set a subject).
Inline content might also set an object, if
@content
is not present, but
@property
is present.
8.1
Changing the evaluation context
8.1.1
Setting the current subject
When triples are created they will always be in relation to a subject resource which is provided either by
new subject
(if there are rules on the current element that have set a subject) or
parent subject
, as passed in via the
evaluation context
. This section looks at the specific ways in which these values are set. Note that it doesn't matter
how the subject is set, so in this section we use the idea of the
current subject
which may be
either
new subject
or
parent subject
8.1.1.1
The current document
When parsing begins, the
current subject
will be the URI of the document being parsed,
or a value as set by a Host Language-provided mechanism such
as the
base
element in (X)HTML. This
means that any metadata found in the
head
of the document will concern the
document itself:

Jo's Friends and Family Blog

...

This would generate the following triples:
<> foaf:primaryTopic <#bbq> .
<> dc:creator "Jo" .
It is possible for the data to appear elsewhere in the document:

Jo's Blog

Jo
's blog

Welcome to my blog.

which would still generate the triple:
<> dc:creator "Jo" .
In (X)HTML the value of
base
may change the initial value of
current subject

Jo's Friends and Family Blog

...

An RDFa Processor should now generate the following triples, regardless of the URL from which the document is served:
foaf:primaryTopic <#bbq> .
dc:creator "Jo" .
8.1.1.2
Using
@about
As processing progresses, any
@about
attributes will change the
current subject
. The value of
@about
is a URI or a CURIE. If it is a relative URI then it needs to be resolved
against the current
base
value. To illustrate how this affects the statements, note in this markup
how the properties inside the (X)HTML
body
element become part of a new calendar event object, rather
than referring to the document as they do in the head of the document:

Jo's Friends and Family Blog

about="#bbq"
typeof="cal:Vevent"
I'm holding
property="cal:summary"
one last summer barbecue
,
on
property="cal:dtstart"
content="2015-09-16T16:00:00-05:00"
datatype="xsd:dateTime">
September 16th at 4pm
.

With this markup an RDFa Processor will generate the following triples:
<> foaf:primaryTopic <#bbq> .
<> dc:creator "Jo" .
<#bbq> rdf:type cal:Vevent .
<#bbq> cal:summary "one last summer barbecue" .
<#bbq> cal:dtastart "2015-09-16T16:00:00-05:00"^^xsd:dateTime .
Other kinds of resources can be used to set the
current subject
, not just references to web-pages. Although not advised,
email addresses might be used to represent a person:
John knows
about="mailto:john@example.org"
rel="foaf:knows" href="mailto:sue@example.org">Sue.

Sue knows
about="mailto:sue@example.org"
rel="foaf:knows" href="mailto:jim@example.org">Jim.
This should generate the following triples:
foaf:knows .
foaf:knows .
Similarly, authors may make statements about images:
about="photo1.jpg"
this photo was taken by
Mark Birbeck

which should generate the following triples:
dc:creator "Mark Birbeck" .
8.1.1.3
Using
@src
If
@about
is not present, then
@src
is next in priority order, for
setting the subject of a statement. A typical use would be to indicate the licensing type of an image:
src="photo1.jpg"
rel="license"
resource="http://creativecommons.org/licenses/by/2.0/" />
Since there is no difference between
@src
and
@about
, then the information expressed in the last
example in the section on
@about
(the
creator
of an image), could be expressed as follows:
rel="license" resource="http://creativecommons.org/licenses/by/2.0/"
property="dc:creator" content="Mark Birbeck"
/>
Since normal chaining rules will apply, the image URL can also be used to complete hanging triples:

src="photo1.jpg"
rel="license" resource="http://creativecommons.org/licenses/by/2.0/"
property="dc:creator" content="Mark Birbeck"
/>

The complete markup yields three triples:
foaf:img .
xhv:license .
dc:creator "Mark Birbeck" .
8.1.1.4
Creating a new item with
@typeof
Whilst
@about
explicitly creates a new context for statements,
@typeof
does so implicitly.
@typeof
works differently to other ways of setting a predicate since the predicate is always
rdf:type
, which means that the processor only requires one attribute, the value of the type.
Since
@typeof
is setting the type of an item, this means that if no
item exists one should automatically be created. This
involves generating a new
bnode
, and is examined in more detail below; it is
mentioned here because the
bnode
used by the new item will become the subject for further statements.
For example, an author may wish to create markup for a person using the FOAF vocabulary, but without having a clear
identifier for the item:
typeof="foaf:Person"
Albert Einstein
Albert

This markup would cause a
bnode
to be created which has a 'type' of
foaf:Person
, as well as name and given
name properties:
_:a rdf:type foaf:Person .
_:a foaf:name "Albert Einstein" .
_:a foaf:givenname "Albert" .
bnode
is simply a unique identifier that is only available to the processor, not to any external software. By generating
values internally, the processor is able to keep track of properties for
_:a
as being distinct from
_:b
. But by not exposing these values to any external software, it is possible to have complete control over
the identifier, as well as preventing further statements being made about the item.
8.1.1.5
Determining the subject with neither
@about
nor
@typeof
As described in the previous two sections,
@about
will always take precedence and mark a new subject, but if no
@about
value is available then
@typeof
will do the same job, although using an implied identifier,
i.e., a
bnode
But if neither
@about
or
@typeof
are present, there are a number of ways that the subject could
be arrived at. One of these is to 'inherit' the subject from the containing statement, with the value to be inherited set
either explicitly, or implicitly.
Inheriting subject from
@resource
The most usual way that an inherited subject might get set would be when the parent statement has an object that is a
resource. Returning to the earlier example, in which the long name for Germany was added, the following markup was used:

Albert Einstein
1879-03-14

property="dbp:conventionalLongName">Federal Republic of Germany

In an earlier illustration the subject and object for Germany were elided by removing the
@resource
, relying
on the
@about
to set the object:

Albert Einstein
1879-03-14

property="dbp:conventionalLongName">Federal Republic of Germany

but it is also possible for authors to achieve the same effect by removing the
@about
and leaving the
@resource

Albert Einstein
1879-03-14

resource="http://dbpedia.org/resource/Germany"
Federal Republic of Germany

In this situation, all statements that are 'contained' by the object resource representing Germany (the value in
@resource
) will have the same subject, making it easy for authors to add additional statements:

Albert Einstein
1879-03-14

Federal Republic of Germany

Looking at the triples that an RDFa Processor would generate, we can see that we actually have two groups of statements; the
first group are set to refer to the
@about
that contains them:
foaf:name "Albert Einstein" .
dbp:dateOfBirth "1879-03-14"^^xsd:date .
dbp:birthPlace .
whilst the second group refer to the
@resource
that contains them:

dbp:conventionalLongName "Federal Republic of Germany" .

dbp:capital .
Note also that the same principle described here applies to
@src
and
@href
Inheriting an anonymous subject
There will be occasions when the author wants to elide the subject and object as shown above, but is not concerned
to name the resource that is common to the two statements (i.e., the object of the first statement, which is the subject
of the second). For example, to indicate that Einstein was influenced by Spinoza the following markup could well be used:

Albert Einstein
1879-03-14

An RDFa Processor will generate the following triples:

dbp:influenced .
foaf:name "Albert Einstein" .
dbp:dateOfBirth "1879-03-14"^^xsd:date .
However, an author could just as easily say that Spinoza influenced
something by the name of Albert Einstein, that was
born on March 14th, 1879

Albert Einstein
1879-03-14

In RDF terms, the item that 'represents' Einstein is
anonymous
, since it has no URI to identify it. However,
the item is given an
automatically generated
bnode
, and it is onto this identifier that all
child statements are attached:
An RDFa Processor will generate the following triples:
dbp:influenced _:a .
_:a foaf:name "Albert Einstein" .
_:a dbp:dateOfBirth "1879-03-14"^^xsd:date .
Note that the
div
is superfluous, and an RDFa Processor will create the intermediate object even if the element is removed:

Albert Einstein
1879-03-14

An alternative pattern is to
keep
the
div
and move the
@rel
onto it:

rel="dbp:influenced"
Albert Einstein
1879-03-14

From the point of view of the markup, this latter layout is to be preferred, since it draws attention to the 'hanging
rel'. But from the point of view of an RDFa Processor, all of these permutations need to be supported.
8.2
Completing 'incomplete triples'
When a new subject is calculated, it is also used to complete any incomplete
triples that are pending. This situation arises when the author wants to 'chain' a number of statements together. For
example, an author could have a statement that Albert Einstein was born in Germany:

Albert Einstein
1879-03-14

and then a further statement that the 'long name' for Germany is the
Federal Republic of Germany
property="dbp:conventionalLongName">Federal Republic of Germany
RDFa allows authors to insert this statement as a self-contained unit into other contexts:

Albert Einstein
1879-03-14

property="dbp:conventionalLongName">Federal Republic of Germany

But it also allows authors to avoid unnecessary repetition and to 'normalize' out duplicate identifiers, in this case the
one for Germany:

Albert Einstein
1879-03-14

property="dbp:conventionalLongName">Federal Republic of Germany

When this happens the
@rel
for 'birth place' is regarded as a 'hanging rel' because it has not yet generated
any triples, but these 'incomplete triples' are completed by the
@about
that appears on the next line. The first
step is therefore to store the two parts of the triple that the RDFa Processor
does
have, but without an object:
dbp:birthPlace
Then as processing continues, the RDFa Processor encounters the subject of the statement about the long name for Germany, and this is
used in two ways. First it is used to complete the 'incomplete triple':
dbp:birthPlace

and second it is used to generate its own triple:
dbp:conventionalLongName "Federal Republic of Germany" .
Note that each occurrence of
@about
will complete any incomplete triples. For example, to mark up the fact that
Albert Einstein had both German and American citizenship, an author need only specify one
@rel
value that is then
used with multiple
@about
values:

In this example there is one incomplete triple:
dbp:citizenship
When the processor meets each of the
@about
values, this triple is completed, giving:

dbp:citizenship

dbp:citizenship

These examples show how
@about
completes triples, but there are other situations that can have the same effect.
For example, when
@typeof
creates a new
bnode
(as described above), that will be used to complete any 'incomplete
triples'. To illustrate,
to indicate that Spinoza influenced both Einstein and Schopenhauer, the following markup could be used:

typeof="foaf:Person"
Albert Einstein
1879-03-14

typeof="foaf:Person"
Arthur Schopenhauer
1788-02-22

First the following incomplete triple is stored:
dbp:influenced
Then when the RDFa Processor processes the two occurrences of
@typeof
, each generates a
bnode
, which is used to both
complete the 'incomplete triple', and to set the subject for further statements:
dbp:influenced
_:a
_:a
rdf:type foaf:Person .
_:a
foaf:name "Albert Einstein" .
_:a
dbp:dateOfBirth "1879-03-14"^^xsd:date .
dbp:influenced
_:b
_:b
rdf:type foaf:Person .
_:b
foaf:name "Arthur Schopenhauer" .
_:b
dbp:dateOfBirth "1788-02-22"^^xsd:date .
Triples are also 'completed' if any one of
@property
@rel
or
@rev
are present. However,
unlike the situation when
@about
or
@typeof
are present, all predicates are attached to one
bnode

Albert Einstein
1879-03-14

This example has two 'hanging rels', and so two situations when 'incomplete triples' will be created. Processing would proceed
as follows; first an incomplete triple is stored:
dbp:influenced
Next, the RDFa Processor processes the predicate values for
foaf:name
dbp:dateOfBirth
and
dbp:citizenship
, but note that only the first needs to 'complete' the 'hanging rel'. So processing
foaf:name
generates two triples:
dbp:influenced
_:a
_:a
foaf:name "Alber Einstein" .
but processing
dbp:dateOfBirth
generates only one:
_:a
dbp:dateOfBirth "1879-03-14"^^xsd:date .
Processing
dbp:citizenship
also uses the same
bnode
, but note that it also generates its own 'incomplete
triple':
_:a dbp:citizenship
As before, the two occurrences of
@about
complete the 'incomplete triple', once each:
_:a dbp:citizenship

_:a dbp:citizenship

The entire set of triples that an RDFa Processor should generate are as follows:
dbp:influenced
_:a
_:a
foaf:name "Alber Einstein" .
_:a
dbp:dateOfBirth "1879-03-14"^^xsd:date .
_:a
dbp:citizenship .
_:a
dbp:citizenship .
8.3
Object resolution
Although objects have been discussed in the previous sections, as part of the explanation of subject resolution, chaining,
evaluation contexts, and so on, this section will look at objects in more detail.
There are two types of object,
URI resource
s and
literal
s.
literal
object can be set by using
@property
to express a
predicate
, and then using either
@content
or the inline text of the element that
@property
is on.
Note that the use of
@content
prohibits the inclusion of rich markup in your literal.
If the inline content of an element accurately represents the object,
then documents should rely upon that rather than duplicating that data using the
@content
URI resource
object can be set
using one of
@rel
or
@rev
to express a
predicate
and then
either
using one of
@href
@resource
or
@src
to provide an object resource explicitly,
or
using
the chaining techniques described above to obtain an object from a nested
subject, or from a
bnode
8.3.1
Literal object resolution
An
object literal
will be generated when
@property
is present.
@property
provides the predicate, and the following sections describe
how the actual literal to be generated is determined.
8.3.1.1
Plain Literals
@content
can be used to indicate a
plain literal
, as follows:
property="dc:creator"
content="Mark Birbeck"
/>
The
plain literal
can also be specified by using the content of the element:
property="dc:creator">
Mark Birbeck

Both of these examples give the following triple:
dc:creator "Mark Birbeck" .
The value of
@content
is given precedence
over any element content, so the following would give exactly the same
triple as shown above:
property="dc:creator"
content="Mark Birbeck"
>John Doe
Language Tags
RDF allows
plain literal
s to have a language tag, as
illustrated by the following example from
RDF-TESTCASES
]:

"chat"
@fr
In RDFa the Host Language may provide a mechanism for
setting the language tag. In XHTML+RDFa [
XHTML-RDFA
], for example,
the XML language attribute
@xml:lang
or
the attribute
@lang
is used to add this information, whether the plain literal is
designated by
@content
, or by the inline
text of the element:
property="ex:property"
xml:lang="fr"
content="chat" />
Note that the language value can be inherited as defined in [
XML10-4e
],
so the following syntax will give the
same triple as above:
prefix="ex: http://www.example.com/ns/"
xml:lang="fr"

Example
property="ex:property" content="chat" />

...

8.3.1.2
Typed literals
Literals can be given a data type using
@datatype
This can be represented in RDFa as follows:
datatype="xsd:dateTime"
September 16th at 4pm
.
The triples that this markup generates include the datatype after the literal:
<> cal:dtstart "2015-09-16T16:00:00-05:00"^^
xsd:dateTime
8.3.1.3
XML Literals
XML documents cannot contain XML markup in their
attributes, which means it is not possible to represent XML within
@content
(the following would cause an
XML parser to generate an error):

content="E = mc²: The Most Urgent Problem of Our Time"
/>

It does not help to escape the content, since the output would
simply be a string of text containing numerous ampersands:
<> dc:title "E = mc
<sup>2</sup>
: The Most Urgent Problem of Our Time" .
RDFa therefore supports the use of normal markup to express XML literals, by using
@datatype

E = mc²: The Most Urgent Problem of Our Time

This would generate the following triple, with the XML preserved in the literal:
<> dc:title "E = mc²: The Most Urgent Problem of Our Time"^^rdf:XMLLiteral .
Note that this requires that a URI mapping for the prefix
rdf
has been defined.
To make authoring easier, if there are child elements and no
@datatype
attribute,
then the effect is the same as if
@datatype
have been explicitly set to
rdf:XMLLiteral

E = mc²: The Most Urgent Problem of Our Time

In the examples given here the
sup
element is actually part of the meaning
of the literal, but there will be situations where the extra markup means nothing, and
can therefore be ignored. In this situation an empty
@datatype
value
can be used to override the XML literal behaviour:

You searched for Einstein:

datatype=""
>Albert Einstein
(b. March 14, 1879, d. April 18, 1955) was a German-born theoretical physicist.

Although the rendering of this page has highlighted the term the user searched for,
setting
@datatype
to nothing ensures that the data is interpreted as a plain
literal, giving the following triples:
foaf:name
"Albert Einstein"
Note that the value of this
XML Literal
is the exclusive
canonicalization [
XML-EXC-C14N
] of the RDFa element's value.
Although the RDFa processing model requires visiting each
element in the tree, if the processor meets an
XML literal
then it
must not
process any further down the tree. This is to prevent triples being generated from markup that is not actually
in the hierarchy. For example, we might want to set the
title of something to some markup that itself includes RDFa:
property="dc:title"
Example 3: ...

In this example the nested RDFa should not be parsed. This effectively means that the presence of
@property
without
@content
will inhibit
any further processing, so authors
should watch out for stray attributes, especially if they find that they are getting fewer triples than they had
expected.
8.3.2
URI object resolution
Most of the rules governing the processing of objects that are resources are to be found in the processing descriptions
given above, since they are important for establishing the subject. This section aims to highlight general concepts, and
anything that might have been missed.
One or more
URI object
s are needed when
@rel
or
@rev
is present. Each attribute
will cause triples to be generated when used with
@href
@resource
or
@src
, or
with the subject value of any nested statement if none of these attributes are present.
@rel
and
@rev
are essentially the inverse of each other; whilst
@rel
establishes a relationship between the
current subject
as subject, and the
current object resource
as the object,
@rev
does the exact opposite, and uses the
current object resource
as the subject, and the
current subject
as the object.
8.3.2.1
Using
@resource
to set the object
RDFa provides the
@resource
attribute as a way to set the object of
statements. This is particularly useful when referring to resources that are not
themselves navigable links:

On Crime and Punishment

resource="urn:ISBN:0140449132"

Rodion Romanovitch! My dear friend! If you go on in this way
you will go mad, I am positive! Drink, pray, if only a few drops!

The
blockquote
element generates the following triple:

.
8.3.2.2
Using
@href
If no
@resource
is present, then
@href
is next in priority order, for setting the object.
When a predicate has been expressed using
@rel
, the
@href
on the [RDFa
statement]'s element is used to identify the object with a [URI
reference]. Its type is a URI:
rel="foaf:knows" href="mailto:sue@example.org"
/>
It's also possible to use both
@rel
and
@rev
at the same time on
an element. This is particularly useful when two things stand in two different relationships
with each other, for example when a picture is taken
by
Mark, but that picture also
depicts
him:

rel="dc:creator" rev="foaf:img"
href="http://www.blogger.com/profile/1109404" />
which then yields two triples:

dc:creator .

foaf:img .
8.3.2.3
Incomplete triples
When a triple predicate has been expressed using
@rel
or
@rev
but no
@href
@src
or
@resource
exists on
the same element, there is a 'hanging rel'. This causes the current subject and
all possible predicates (with an indicator of whether they are 'forwards, i.e.,
@rel
values,
or not, i.e.,
@rev
values), to be stored as 'incomplete triples' pending discovery of a subject
that could be used to 'complete' those triples.
This process is described in more detail in
Completing 'Incomplete Triples'
9.
RDFa Profiles
RDFa Profiles are optional external documents that define collections of terms
and/or prefix mappings. These documents
must
be defined in an
approved RDFa Host Language (currently XHTML+RDFa [
XHTML-RDFA
]).
They
may
also be defined in other RDF serializations as well
(e.g., RDF/XML [
RDF-SYNTAX-GRAMMAR
] or Turtle [
TURTLE
]).
RDFa Profiles are referenced via
@profile
, and can
be used by document authors to simplify the task of adding semantic markup. When an
RDFa document includes
@profile
, the value of the attribute is evaluated in
order. For each URI in the value, do the following:
Attempt to retrieve the content of the
URI. If the retrieval fails, continue with the next URI in the value.
Otherwise, parse the retrieved content as an RDFa document (according to the
processing rules in that document's Host Language specification) and extract the triples
into a collection associated with that URI. Note: These triples
must not
be co-mingled
with the triples being extracted from any other URI.
For every extracted triple that
is the common subject of an
rdfa:prefix
and an
rdfa:uri
predicate,
create a mapping from the object literal of the
rdfa:prefix
predicate to the
object literal of the
rdfa:uri
predicate. Add or update this mapping in the
local list of URI mappings
after transforming the 'prefix' component to
lower-case.
For every extracted triple that
is the common subject of an
rdfa:term
and an
rdfa:uri
predicate,
create a mapping from the object literal of the
rdfa:term
predicate to the
object literal of the
rdfa:uri
predicate. Add or update this mapping in the
local term mappings
Once all the URIs in the
@profile
value have been processed, continue
with the normal processing of the
current element
It is possible that a referenced RDFa document will in turn reference
other documents via
@profile
. Regardless of the depth to which such
references might go, only the triples in the top level document effect current
processing.
RDFa Processor developers are permitted and encouraged to cache the
relevant triples retrieved via this mechanism, including embedding definitions for well known vocabularies in the implementation if appropriate.
If one of the objects is not a Literal or if there are additional
rdfa:uri
or
rdfa:term
predicates sharing the same subject, no mapping is created.
A.
CURIE Datatypes
In order to facilitate the use of CURIEs in markup languages, this
specification defines some additional datatypes in the XHTML datatype
space (
).
Markup languages that want to import these
definitions can find them in the
"datatypes" file for their schema grammar:
DTD xhtml-datatypes.mod
XML Schema xhtml-datatypes.xsd
Specifically, the following datatypes are defined:
CURIE
A single
curie
CURIEs
A whitespace separated list of CURIEs
CURIEorURI
CURIE
or a
URI
CURIEorURIs
A whitespace separated list of
CURIEorURI
SafeCURIE
A single
safe_curie
SafeCURIEorCURIEorURI
A single
SafeCURIE
or
CURIEorURI
SafeCURIEorCURIEorURIs
A whitespace separated list of
SafeCURIEorCURIEorURI
s.
TERM
A single
term
TERMorCURIEorURI
TERM
or a
CURIEorURI
TERMorCURIEorURIs
A whitespace separated list of
TERMorCURIEorURI
The datatypes
TERMorCURIEorURI
and
TERMorCURIEorURIs
are defined such that
an RDFa Processor
must
first evaluate the attribute value
to determine if it is a
TERM
. If it does not match the production
rules for
TERM
, then an RDFa Processor
must
evaluate the attribute
value to determine if it matches the production for
CURIEorURI
A.1
XML Schema Definition
This section is non-normative.
The following
informative
XML Schema definition for these datatypes is included as an example:

xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="http://www.w3.org/1999/xhtml/datatypes/"
xmlns:xh11d="http://www.w3.org/1999/xhtml/datatypes/"
targetNamespace="http://www.w3.org/1999/xhtml/datatypes/"
elementFormDefault="qualified"

A.2
XML DTD Definition
This section is non-normative.
The following
informative
XML DTD definition for these datatypes is included as an example:

B.
The RDFa Term Assignment Vocabulary
The RDFa Term Assignment Vocabulary is used to modify RDFa processing behavior.
Its URI is
The Vocabulary includes the following term definitions (shown here in Turtle [
TURTLE
] format):
@prefix
rdf: .
@prefix
rdfs: .
@prefix
owl: .
@prefix
rdfa: .

rdfa:VocabularyMapping a rdfs:Class .

rdfa:PrefixMapping a rdfs:Class;
rdfs:subClassOf rdfa:VocabularyMapping .

rdfa:TermMapping a rdfs:Class ;
rdfs:subClassOf rdfa:VocabularyMapping .

[] a owl:AllDisjointClasses ;
owl:members ( rdfa:PrefixMapping rdfa:TermMapping ) .

rdfa:uri a rdf:Property, owl:FunctionalProperty, owl:DatatypeProperty ;
rdfs:range xsd:anyURI ;
rdfs:domain rdfa:VocabularyMapping .

rdfa:prefix a rdf:Property, owl:FunctionalProperty, owl:DatatypeProperty ;
rdfs:range xsd:NMTOKEN ;
rdfs:domain rdfa:PrefixMapping .

rdfa:term a rdf:Property, owl:FunctionalProperty, owl:DatatypeProperty ;
rdfs:range xsd:NMTOKEN ;
rdfs:domain rdfa:TermMapping .
This vocabulary is also available in an
separate file
in Turtle format and in
RDF/XML format
These predicates can be used to 'pair' URI strings and their usage in the form of a prefix and/or a
term as part of, for example, a blank node. An example can be as follows:
rdfa:uri "http://xmlns.com/foaf/0.1/name" ;
rdfa:prefix "foaf"
which defines a prefix for the foaf URI.
an RDFa version of the vocabulary
should be provided - we still need to write it.
C.
Change History
This section is non-normative.
2010p>2010-02-25: Split into RDFa Core and XHTML+RDFa.
2010-01-01: Applied changes to start production of version 1.1.
This includes the re-integration of datatype CURIEorURI.
D.
Acknowledgments
This section is non-normative.
At the time of publication, the members of the
RDFa Working Group were:
Ben Adida, Creative Commons (Co-Chair)
Benjamin Adrian, German Research Center for Artificial Intelligence (DFKI) Gmbh
Mark Birbeck, webBackplane.com (Invited Expert)
Abhijit Galkward, Rochester Institute of Technology
Markus Gylling, DAISY Consortium
Ivan Herman,
W3C
Toby Inkster (Invited Expert)
Shane McCarron, Applied Testing and Technology, Inc. (Invited Expert)
Knud Möller (DERI Galway at the National University of Ireland)
John O'Donovan, British Broadcasting Corporation
Steven Pemberton, Centre for Mathematics and Computer Science (CWI)
Jeffrey Sonstein, Rochester Institute of Technology
Manu Sporny, Digital Bazaar (Co-Chair, Invited Expert)
Robert Weir, IBM Corporation
E.
References
E.1
Normative references
[RDF-SYNTAX-GRAMMAR]
Dave Beckett.
RDF/XML Syntax Specification (Revised).
10 February 2004. W3C Recommendation. URL:
[RFC2119]
S. Bradner.
Key words for use in RFCs to Indicate Requirement Levels.
Internet RFC 2119. URL:
[RFC3987]
M. Dürst; M. Suignard.
Internationalized Resource Identifiers (IRIs).
January 2005. Internet RFC 3987. URL:
[URI]
T. Berners-Lee; R. Fielding; L. Masinter.
Uniform Resource Identifiers (URI): generic syntax.
January 2005. Internet RFC 3986. URL:
[XHTML-RDFA]
Shane McCarron, et. al.
XHTML+RDFa 1.1.
30 March 2010. W3C Editor's Draft. URL:
[XML-NAMES]
Richard Tobin; et al.
Namespaces in XML 1.0 (Second Edition).
16 August 2006. W3C Recommendation. URL:
[XML10-4e]
C. M. Sperberg-McQueen; et al.
Extensible Markup Language (XML) 1.0 (Fourth Edition).
16 August 2006. W3C Recommendation. URL:
[XMLSCHEMA-2]
Paul V. Biron; Ashok Malhotra.
XML Schema Part 2: Datatypes Second Edition.
28 October 2004. W3C Recommendation. URL:
E.2
Informative references
[HTML401]
David Raggett; Ian Jacobs; Arnaud Le Hors.
HTML 4.01 Specification.
24 December 1999. W3C Recommendation. URL:
[MICROFORMATS]
Microformats
. URL:
[RDF-CONCEPTS]
Graham Klyne; Jeremy J. Carroll.
Resource Description Framework (RDF): Concepts and Abstract Syntax.
10 February 2004. W3C Recommendation. URL:
[RDF-PRIMER]
Frank Manola; Eric Miller.
RDF Primer.
10 February 2004. W3C Recommendation. URL:
[RDF-SYNTAX]
Ora Lassila; Ralph R. Swick.
Resource Description Framework (RDF) Model and Syntax Specification.
22 February 1999. W3C Recommendation. URL:
[RDF-TESTCASES]
Jan Grant; Dave Beckett.
RDF Test Cases.
10 February 2004. W3C Recommendation. URL:
[RDFA-PRIMER]
Mark Birbeck; Ben Adida.
RDFa Primer.
14 October 2008. W3C Note. URL:
[RDFA-SYNTAX]
Ben Adida, et al.
RDFa in XHTML: Syntax and Processing.
14 October 2008. W3C Recommendation. URL:
[RELAXNG-SCHEMA]
Information technology -- Document Schema Definition Language (DSDL) -- Part 2: Regular-grammar-based validation -- RELAX NG
. ISO/IEC 19757-2:2008. URI:
[SAX]
D. Megginson, et al.
SAX: The Simple API for XML
. May 1998. URL:
[TURTLE]
David Beckett, Tim Berners-Lee.
Turtle: Terse RDF Triple Language
January 2008. W3C Team Submission. URL:
[XHTML11]
Murray Altheim; Shane McCarron.
XHTML™ 1.1 - Module-based XHTML.
31 May 2001. W3C Recommendation. URL:
[XML-EXC-C14N]
Donald E. Eastlake 3rd; Joseph Reagle; John Boyer.
Exclusive XML Canonicalization Version 1.0.
18 July 2002. W3C Recommendation. URL:

Same domain → Similar titles →

RDFa Core 1.1

Jo's blog

E = mc2: The Most Urgent Problem of Our Time

E = mc2: The Most Urgent Problem of Our Time

Jo
's blog

E = mc²: The Most Urgent Problem of Our Time

E = mc²: The Most Urgent Problem of Our Time