HTML RDFa5

Abstract

This specification defines the HTML RDFa5 mechanism. This mechanism allows machine-readable data to be embedded in HTML documents in an easy-to-write manner, with an unambiguous parsing model. It is compatible with numerous other data formats including RDF and JSON.

Table of Contents

1. 1 Common infrastructure
   1. 1.1 Dependencies
   2. 1.2 Terminology
   3. 1.3 Conformance requirements
   4. 1.4 HTMLPropertiesCollection
2. 2 Introduction
   1. 2.1 Overview
   2. 2.2 The basic syntax
   3. 2.3 Typed items
   4. 2.4 Global identifiers for items
   5. 2.5 Selecting names when defining vocabularies
   6. 2.6 Using the RDFa5 DOM API
3. 3 Encoding RDFa5
   1. 3.1 The RDFa5 model
   2. 3.2 Items
   3. 3.3 Names: the rdfpredicate attribute
   4. 3.4 Values
   5. 3.5 Associating names with items
4. 4 RDFa5 DOM API
5. 5 Other changes to HTML5
   1. 5.1 Content models
   2. 5.2 Drag-and-drop
6. 6 Converting HTML to other formats
   1. 6.1 JSON
   2. 6.2 RDF
      1. 6.2.1 Examples
7. 7 IANA considerations
   1. 7.1 application/RDFa5+json
8. References
9. Acknowledgements

1 Common infrastructure

1.1 Dependencies

This specification depends on the Web IDL and HTML5 specifications. [WEBIDL] [HTML5]

1.2 Terminology

This specification relies heavily on the HTML5 specification to define underlying terms.

HTML5 defines the concept of DOM collections, and of IDL attributes reflecting content attributes. It also defines tree order and the concept of a node's home subtree.

HTML5 defines the terms URL, valid URL, absolute URL, and resolve a URL.

HTML5 defines the terms alphanumeric ASCII characters, space characters split a string on spaces, converted to ASCII uppercase, and prefix match.

HTML5 defines the meaning of the term HTML element, as well as all the elements referenced in this specification. It defines the specific concept of the title element in the context of a Document. In the context of content models it defines the terms flow content and phrasing content. It also defines what an element's ID or language is in HTML.

HTML5 defines the set of global attributes, as well as terms used in describing attributes and their processing, such as the concept of a boolean attribute, of an unordered set of unique space-separated tokens, of a valid non-negative integer, of a date, a time, a global date and time, a valid date string, and a valid global date and time string.

HTML5 defines what the document's current address is.

Finally, HTML5 also defines the concepts of drag-and-drop initialization steps and of the list of dragged nodes, which come up in the context of drag-and-drop interfaces.

1.3 Conformance requirements

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).

There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.

1.4 HTMLPropertiesCollection

The HTMLPropertiesCollection interface represents a collection of elements that add name-value pairs to a particular item in the RDFa5 model.

interface HTMLPropertiesCollection : HTMLCollection {
  // inherits length and item()
  caller getter PropertyNodeList namedItem(in DOMString name); // overrides inherited namedItem()
  readonly attribute DOMStringList names;
};

typedef sequence<any> PropertyValueArray;

interface PropertyNodeList : NodeList {
  readonly attribute PropertyValueArray values;
};

collection . length

Returns the number of elements in the collection.

element = collection . item(index)

collection[index]

collection(index)

Returns the element with index index from the collection. The items are sorted in tree order.

Returns null if index is out of range.

propertyNodeList = collection . namedItem(name)

collection[name]

collection(name)

Returns a PropertyNodeList object containing any elements that add a property named name.

collection . names

Returns a DOMStringList with the property names of the elements in the collection.

propertyNodeList . values

Returns an array of the various values that the relevant elements have.

2 Introduction

2.1 Overview

This section is non-normative.

Sometimes, it is desirable to annotate content with specific machine-readable labels, e.g. to allow generic scripts to provide services that are customised to the page, or to enable content from a variety of cooperating authors to be processed by a single script in a consistent manner.

For this purpose, authors can use the RDFa5 features described in this section. RDFa5 allows nested groups of name-value pairs to be added to documents, in parallel with the existing content.

2.2 The basic syntax

This section is non-normative.

At a high level, RDFa5 consists of a group of name-value pairs. The groups are called items, and each name-value pair is a property. Items and properties are represented by regular elements.

To create an item, the rdfbase attribute is used.

To add a property to an item, the rdfpredicate attribute is used on one of the item's descendants.

<div rdfbase>
 <p>My name is <span rdfpredicate="name">Elizabeth</span>.</p>
</div>

<div rdfbase>
 <p>My name is <span rdfpredicate="name">Daniel</span>.</p>
</div>

Properties generally have values that are strings.

<div rdfbase>
 <p>My name is <span rdfpredicate="name">Neil</span>.</p>
 <p>My band is called <span rdfpredicate="band">Four Parts Water</span>.</p>
 <p>I am <span rdfpredicate="nationality">British</span>.</p>
</div>

Properties can also have values that are URLs. This is achieved using the a element and its href attribute, the img element and its src attribute, or other elements that link to or embed external resources.

<div rdfbase>
 <img rdfpredicate="image" src="google-logo.png" alt="Google">
</div>

Properties can also have values that are dates, times, or dates and times. This is achieved using the time element and its datetime attribute.

<div rdfbase>
 I was born on <time rdfpredicate="birthday" datetime="2009-05-10">May 10th 2009</time>.
</div>

Properties can also themselves be groups of name-value pairs, by putting the rdfbase attribute on the element that declares the property.

Items that are not part of others are called top-level RDFa5 items.

<div rdfbase>
 <p>Name: <span rdfpredicate="name">Amanda</span></p>
 <p>Band: <span rdfpredicate="band" rdfbase> <span rdfpredicate="name">Jazz Band</span> (<span rdfpredicate="size">12</span> players)</span></p>
</div>

Properties that are not descendants of the element with the rdfbase attribute can be associated with the item using the rdfinclude attribute. This attribute takes a list of IDs of elements to crawl in addition to crawling the children of the element with the rdfbase attribute.

<div rdfbase id="amanda" rdfinclude="a b"></div>
<p id="a">Name: <span rdfpredicate="name">Amanda</span></p>
<div id="b" rdfpredicate="band" rdfbase rdfinclude="c"></div>
<div id="c">
 <p>Band: <span rdfpredicate="name">Jazz Band</span></p>
 <p>Size: <span rdfpredicate="size">12</span> players</p>
</div>

An item can have multiple properties with the same name and different values.

<div rdfbase>
 <p>Flavors in my favorite ice cream:</p>
 <ul>
  <li rdfpredicate="flavor">Lemon sorbet</li>
  <li rdfpredicate="flavor">Apricot sorbet</li>
 </ul>
</div>

An element introducing a property can also introduce multiple properties at once, to avoid duplication when some of the properties have the same value.

<div rdfbase>
 <span rdfpredicate="favorite-color favorite-fruit">orange</span>
</div>

It's important to note that there is no relationship between the RDFa5 and the content of the document where the RDFa5 is marked up.

<figure>
 <img src="castle.jpeg">
 <figcaption><span rdfbase><span rdfpredicate="name">The Castle</span></span> (1986)</figcaption>
</figure>

<span rdfbase><meta rdfpredicate="name" content="The Castle"></span>
<figure>
 <img src="castle.jpeg">
 <figcaption>The Castle (1986)</figcaption>
</figure>

2.3 Typed items

This section is non-normative.

The examples in the previous section show how information could be marked up on a page that doesn't expect its RDFa5 to be re-used. RDFa5 is most useful, though, when it is used in contexts where other authors and readers are able to cooperate to make new uses of the markup.

For this purpose, it is necessary to give each item a type, such as "http://example.com/person", or "http://example.org/cat", or "http://band.example.net/". Types are identified as URLs.

The type for an item is given as the value of an rdfvocab attribute on the same element as the rdfbase attribute.

<section rdfbase rdfvocab="http://example.org/animals#cat">
 <h1 rdfpredicate="name">Hedral</h1>
 <p rdfpredicate="desc">Hedral is a male american domestic
 shorthair, with a fluffy black fur with white paws and belly.</p>
 <img rdfpredicate="img" src="hedral.jpeg" alt="" title="Hedral, age 18 months">
</section>

An item can only have one type. The type gives the context for the properties, thus defining a vocabulary: a property named "class" given for an item with the type "http://census.example/person" might refer to the economic class of an individual, while a property named "class" given for an item with the type "http://example.com/school/teacher" might refer to the classroom a teacher has been assigned.

2.4 Global identifiers for items

This section is non-normative.

Sometimes, an item gives information about a topic that has a global identifier. For example, books can be identified by their ISBN number.

Vocabularies (as identified by the rdfvocab attribute) can be designed such that items get associated with their global identifier in an unambiguous way by expressing the global identifiers as URLs given in an rdfsubject attribute.

The exact meaning of the URLs given in rdfsubject attributes depends on the vocabulary used.

<dl rdfbase
    rdfvocab="http://vocab.example.net/book"
    rdfsubject="urn:isbn:0-330-34032-8">
 <dt>Title
 <dd rdfpredicate="title">The Reality Dysfunction
 <dt>Author
 <dd rdfpredicate="author">Peter F. Hamilton
 <dt>Publication date
 <dd><time rdfpredicate="pubdate" datetime="1996-01-26">26 January 1996</time>
</dl>

2.5 Selecting names when defining vocabularies

This section is non-normative.

Using RDFa5 means using a vocabulary. For some purposes, an ad-hoc vocabulary is adequate. For others, a vocabulary will need to be designed. Where possible, authors are encouraged to re-use existing vocabularies, as this makes content re-use easier.

When designing new vocabularies, identifiers can be created either using URLs, or, for properties, as plain words (with no dots or colons). For URLs, conflicts with other vocabularies can be avoided by only using identifiers that correspond to pages that the author has control over.

Properties whose names are just plain words can only be used within the context of the types for which they are intended; properties named using URLs can be reused in items of any type. If an item has no type, and is not part of another item, then if its properties have names that are just plain words, they are not intended to be globally unique, and are instead only intended for limited use. Generally speaking, authors are encouraged to use either properties with globally unique names (URLs) or ensure that their items are typed.

<section rdfbase rdfvocab="http://example.org/animals#cat">
 <h1 rdfpredicate="name http://example.com/fn">Hedral</h1>
 <p rdfpredicate="desc">Hedral is a male american domestic
 shorthair, with a fluffy <span
 rdfpredicate="http://example.com/color">black</span> fur with <span
 rdfpredicate="http://example.com/color">white</span> paws and belly.</p>
 <img rdfpredicate="img" src="hedral.jpeg" alt="" title="Hedral, age 18 months">
</section>

2.6 Using the RDFa5 DOM API

This section is non-normative.

The RDFa5 becomes even more useful when scripts can use it to expose information to the user, for example offering it in a form that can be used by other applications.

The document.getItems(typeNames) method provides access to the top-level RDFa5 items. It returns a NodeList containing the items with the specified types, or all types if no argument is specified.

Each item is represented in the DOM by the element on which the relevant rdfbase attribute is found. These elements have their element.rdfbase IDL attribute set to true.

The type of items can be obtained using the element.rdfvocab IDL attribute on the element with the rdfbase attribute.

var cats = document.getItems("http://example.com/feline");

Once an element representing an item has been obtained, its properties can be extracted using the properties IDL attribute. This attribute returns an HTMLPropertiesCollection, which can be enumerated to go through each element that adds one or more properties to the item. It can also be indexed by name, which will return an object with a list of the elements that add properties with that name.

Each element that adds a property also has a itemValue IDL attribute that returns its value.

var user = document.getItems('http://example.net/user')[0];
alert('Hello ' + user.properties['name'][0].content + '!');

The HTMLPropertiesCollection object, when indexed by name in this way, actually returns a PropertyNodeList object with all the matching properties. The PropertyNodeList object can be used to obtain all the values at once using its values attribute, which returns an array of all the values.

var cat = document.getItems('http://example.org/animals#cat')[0];
var colors = cat.properties['http://example.com/color'].values;
var result;
if (colors.length == 0) {
  result = 'Color unknown.';
} else if (colors.length == 1) {
  result = 'Color: ' + colors[0];
} else {
  result = 'Colors:';
  for (var i = 0; i < colors.length; i += 1)
    result += ' ' + colors[i];
}

It's also possible to get a list of all the property names using the object's names IDL attribute.

var outer = document.createElement('ul');
var items = document.getItems();
for (var item = 0; item < items.length; item += 1) {
  var itemLi = document.createElement('li');
  var inner = document.createElement('ul');
  for (var name = 0; name < items[item].properties.names.length; name += 1) {
    var propLi = document.createElement('li');
    propLi.appendChild(document.createTextNode(items[item].properties.names[name]));
    inner.appendChild(propLi);
  }
  itemLi.appendChild(inner);
  outer.appendChild(itemLi);
}
document.body.appendChild(outer);

<section rdfbase rdfvocab="http://example.org/animals#cat">
 <h1 rdfpredicate="name http://example.com/fn">Hedral</h1>
 <p rdfpredicate="desc">Hedral is a male american domestic
 shorthair, with a fluffy <span
 rdfpredicate="http://example.com/color">black</span> fur with <span
 rdfpredicate="http://example.com/color">white</span> paws and belly.</p>
 <img rdfpredicate="img" src="hedral.jpeg" alt="" title="Hedral, age 18 months">
</section>

3 Encoding RDFa5

The following attributes are added as global attributes to HTML elements:

• rdfsubject
• rdfpredicate
• rdfinclude
• rdfbase
• rdfvocab

3.1 The RDFa5 model

The RDFa5 model consists of groups of name-value pairs known as items.

Each group is known as an item. Each item can have an item type, a global identifier (if the item type supports global identifiers for its items), and a list of name-value pairs. Each name in the name-value pair is known as a property, and each property has one or more values. Each value is either a string or itself a group of name-value pairs (an item).

An item is said to be a typed item when either it has an item type, or it is the value of a property of a typed item. The relevant type for a typed item is the item's item type, if it has one, or else is the relevant type of the item for which it is a property's value.

3.2 Items

Every HTML element may have an rdfbase attribute specified. The rdfbase attribute is a boolean attribute.

An element with the rdfbase attribute specified creates a new item, a group of name-value pairs.

Elements with an rdfbase attribute may have an rdfvocab attribute specified, to give the item type of the item.

The rdfvocab attribute, if specified, must have a value that is a valid URL that is an absolute URL for which the string "http://www.w3.org/1999/xhtml/RDFa5#" is not a prefix match.

The item type of an item is the value of its element's rdfvocab attribute, if it has one and its value is not the empty string. If the rdfvocab attribute is missing or its value is the empty string, the item is said to have no item type.

The item type must be a type defined in an applicable specification.

The rdfvocab attribute must not be specified on elements that do not have an rdfbase attribute specified.

Elements with an rdfbase attribute and an rdfvocab attribute that references a vocabulary that is defined to support global identifiers for items may also have an rdfsubject attribute specified, to give a global identifier for the item, so that it can be related to other items on pages elsewhere on the Web.

The rdfsubject attribute, if specified, must have a value that is a valid URL.

The global identifier of an item is the value of its element's rdfsubject attribute, if it has one, resolved relative to the element on which the attribute is specified. If the rdfsubject attribute is missing or if resolving it fails, it is said to have no global identifier.

The rdfsubject attribute must not be specified on elements that do not have both an rdfbase attribute and an rdfvocab attribute specified, and must not be specified on elements with an rdfbase attribute whose rdfvocab attribute specifies a vocabulary that does not support global identifiers for items, as defined by that vocabulary's specification.

Elements with an rdfbase attribute may have an rdfinclude attribute specified, to give a list of additional elements to crawl to find the name-value pairs of the item.

The rdfinclude attribute, if specified, must have a value that is an unordered set of unique space-separated tokens consisting of IDs of elements in the same home subtree.

The rdfinclude attribute must not be specified on elements that do not have an rdfbase attribute specified.

3.3 Names: the rdfpredicate attribute

Every HTML element may have an rdfpredicate attribute specified, if doing so adds a property to one or more items (as defined below).

The rdfpredicate attribute, if specified, must have a value that is an unordered set of unique space-separated tokens representing the names of the name-value pairs that it adds. The attribute's value must have at least one token.

Each token must be either:

• A valid URL that is an absolute URL for which the string "http://www.w3.org/1999/xhtml/RDFa5#" is not a prefix match, or
• If the item is a typed item: a defined property name allowed in this situation according to the specification that defines the relevant type for the item, or
• If the item is not a typed item: a string that contains no U+002E FULL STOP characters (.) and no U+003A COLON characters (:).

When an element with an rdfpredicate attribute adds a property to multiple items, the requirement above regarding the tokens applies for each item individually.

The property names of an element are the tokens that the element's rdfpredicate attribute is found to contain when its value is split on spaces, with the order preserved but with duplicates removed (leaving only the first occurrence of each name).

Within an item, the properties are unordered with respect to each other, except for properties with the same name, which are ordered in the order they are given by the algorithm that defines the properties of an item.

<div rdfbase>
 <p rdfpredicate="a">1</p>
 <p rdfpredicate="a">2</p>
 <p rdfpredicate="b">test</p>
</div>

<div rdfbase>
 <p rdfpredicate="b">test</p>
 <p rdfpredicate="a">1</p>
 <p rdfpredicate="a">2</p>
</div>

<div rdfbase>
 <p rdfpredicate="a">1</p>
 <p rdfpredicate="b">test</p>
 <p rdfpredicate="a">2</p>
</div>

<div rdfbase rdfinclude="x">
 <p rdfpredicate="b">test</p>
 <p rdfpredicate="a">2</p>
</div>
<div id="x">
 <p rdfpredicate="a">1</p>
</div>

3.4 Values

The property value of a name-value pair added by an element with an rdfpredicate attribute depends on the element, as follows:

If the element also has an rdfbase attribute

The value is the item created by the element.

If the element is a meta element

The value is the value of the element's content attribute, if any, or the empty string if there is no such attribute.

If the element is an audio, embed, iframe, img, source, or video element

The value is the absolute URL that results from resolving the value of the element's src attribute relative to the element at the time the attribute is set, or the empty string if there is no such attribute or if resolving it results in an error.

If the element is an a, area, or link element

The value is the absolute URL that results from resolving the value of the element's href attribute relative to the element at the time the attribute is set, or the empty string if there is no such attribute or if resolving it results in an error.

If the element is an object element

The value is the absolute URL that results from resolving the value of the element's data attribute relative to the element at the time the attribute is set, or the empty string if there is no such attribute or if resolving it results in an error.

If the element is a time element with a datetime attribute

The value is the value of the element's datetime attribute.

Otherwise

The value is the element's textContent.

The URL property elements are the a, area, audio, embed, iframe, img, link, object, source, and video elements.

If a property's value is an absolute URL, the property must be specified using a URL property element.

If a property's value represents a date, time, or global date and time, the property must be specified using the datetime attribute of a time element.

3.5 Associating names with items

To find the properties of an item defined by the element root, the user agent must try to crawl the properties of the element root, with an empty list as the value of memory: if this fails, then the properties of the item defined by the element root is an empty list; otherwise, it is the returned list.

To crawl the properties of an element root with a list memory, the user agent must run the following steps:

1. If root is in memory, then the algorithm fails; abort these steps.

2. Collect all the elements in the item root, and let results be the result.

3. If root is in results, then the algorithm fails; abort these steps.

4. If any elements are listed in results more than once, then the algorithm fails; abort these steps.

5. Remove any elements from results that do not have an rdfpredicate attribute specified.

6. Let new memory be a new list consisting of the old list memory with the addition of root.

7. For each element in results that has an rdfbase attribute specified, crawl the properties of the element, with new memory as the memory. If this fails, then this instance of the algorithm fails as well; abort these steps. (If it succeeds, the return value is discarded.)

8. Sort results in tree order.

9. Return results.

To collect all the elements in the item root, the user agent must run these steps:

1. Let results and pending be empty lists of elements.

2. Add all the children elements of root to pending.

3. If root has an rdfinclude attribute, split the value of that rdfinclude attribute on spaces. For each resulting token ID, if there is an element in the home subtree of root with the ID ID, then add the first such element to pending.

4. Loop: Remove an element from pending and let current be that element.

5. Add current to results.

6. If current does not have an rdfbase attribute, then: add all the child elements of current to pending.

7. End of loop: If pending is not empty, return to the step labeled loop.

8. Return results.

An item is a top-level RDFa5 item if its element does not have an rdfpredicate attribute.

An item is a used RDFa5 item if it is a top-level RDFa5 item, or if it has an rdfpredicate attribute and would be found to be the property of an item that is itself a used RDFa5 item.

A document must not contain any items that are not used RDFa5 items.

A document must not contain any elements that have an rdfpredicate attribute that would not be found to be a property of any of the items in that document were their properties all to be determined.

A document must not contain any items for which crawling the properties of the element, with an empty list as the value of memory, fails.

The algorithms in this section are especially inefficient, in the interests of keeping them easy to understand. Implementors are strongly encouraged to refactor and optimise them in their user agents.

<!DOCTYPE HTML>
<html>
 <head>
  <title>Photo gallery</title>
 </head>
 <body>
  <h1>My photos</h1>
  <figure rdfbase rdfvocab="http://n.whatwg.org/work" rdfinclude="licenses">
   <img rdfpredicate="work" src="images/house.jpeg" alt="A white house, boarded up, sits in a forest.">
   <figcaption rdfpredicate="title">The house I found.</figcaption>
  </figure>
  <figure rdfbase rdfvocab="http://n.whatwg.org/work" rdfinclude="licenses">
   <img rdfpredicate="work" src="images/mailbox.jpeg" alt="Outside the house is a mailbox. It has a leaflet inside.">
   <figcaption rdfpredicate="title">The mailbox.</figcaption>
  </figure>
  <footer>
   <p id="licenses">All images licensed under the <a rdfpredicate="license"
   href="http://www.opensource.org/licenses/mit-license.php">MIT
   license</a>.</p>
  </footer>
 </body>
</html>

<!-- invalid example - do not copy -->
<div rdfbase>
 <span rdfpredicate="example">This is <em>not</em> a property of the
 <code>div</code> element.</span>
 <p rdfpredicate="demo" rdfbase rdfinclude="test thing"> <!-- "thing" is a descendant
                   of "test", which leads to it being included twice, which is invalid -->
  <span rdfpredicate="sample">This isn't part of anything either.</span>
 </p>
</div>
<p id="test">
 <span id="thing">(this element is referenced twice by the
 <code>p</code> above, causing all the items that involve that
 <code>rdfinclude=""</code> attribute to act as if they had no
 properties.)</span>
</p>

4 RDFa5 DOM API

[Supplemental] interface HTMLDocument { 
  NodeList getItems(in optional DOMString typeNames); // RDFa5
};

[Supplemental] interface HTMLElement {
  // RDFa5 
           attribute boolean rdfbase;
           attribute DOMString rdfvocab;
           attribute DOMString rdfsubject;
  [PutForwards=value] readonly attribute DOMSettableTokenList rdfinclude;
  [PutForwards=value] readonly attribute DOMSettableTokenList rdfpredicate;
  readonly attribute HTMLPropertiesCollection properties;
           attribute any itemValue;
};

document . getItems( [ types ] )

Returns a NodeList of the elements in the Document that create items, that are not part of other items, and that are of one of the types given in the argument, if any are listed.

The types argument is interpreted as a space-separated list of types.

element . properties

If the element has an rdfbase attribute, returns an HTMLPropertiesCollection object with all the element's properties. Otherwise, an empty HTMLPropertiesCollection object.

element . itemValue [ = value ]

Returns the element's value.

Can be set, to change the element's value. Setting the value when the element has no rdfpredicate attribute or when the element's value is an item throws an INVALID_ACCESS_ERR exception.

if (element.rdfpredicate.contains('color'))
  count += 1;

for (var index = 0; index < element.rdfinclude.length; index += 1)
  process(document.getElementById(element.rdfinclude[index]));

5 Other changes to HTML5

5.1 Content models

If the rdfpredicate attribute is present on link or meta, they are flow content and phrasing content. The link and meta elements may be used where phrasing content is expected if the rdfpredicate attribute is present.

If a link element has an rdfpredicate attribute, the rel attribute may be omitted.

If a meta element has an rdfpredicate attribute, the name, http-equiv, and charset attributes must be omitted, and the content attribute must be present.

<dl rdfbase
    rdfvocab="http://purl.org/vocab/frbr/core#Work"
    rdfsubject="http://books.example.com/works/45U8QJGZSQKDH8N">
 <dt>Title</dt>
 <dd><cite rdfpredicate="http://purl.org/dc/terms/title">Just a Geek</cite></dd>
 <dt>By</dt>
 <dd><span rdfpredicate="http://purl.org/dc/terms/creator">Wil Wheaton</span></dd>
 <dt>Format</dt>
 <dd rdfpredicate="http://purl.org/vocab/frbr/core#realization"
     rdfbase
     rdfvocab="http://purl.org/vocab/frbr/core#Expression"
     rdfsubject="http://books.example.com/products/9780596007683.BOOK">
  <link rdfpredicate="http://purl.org/dc/terms/type" href="http://books.example.com/product-types/BOOK">
  Print
 </dd>
 <dd rdfpredicate="http://purl.org/vocab/frbr/core#realization"
     rdfbase
     rdfvocab="http://purl.org/vocab/frbr/core#Expression"
     rdfsubject="http://books.example.com/products/9780596802189.EBOOK">
  <link rdfpredicate="http://purl.org/dc/terms/type" href="http://books.example.com/product-types/EBOOK">
  Ebook
 </dd>
</dl>

@prefix dc: <http://purl.org/dc/terms/> .
 @prefix frbr: <http://purl.org/vocab/frbr/core#> .

<http://books.example.com/works/45U8QJGZSQKDH8N> a frbr:Work ;
     dc:creator "Wil Wheaton"@en ;
     dc:title "Just a Geek"@en ;
     frbr:realization <http://books.example.com/products/9780596007683.BOOK>,
         <http://books.example.com/products/9780596802189.EBOOK> . 

<http://books.example.com/products/9780596007683.BOOK> a frbr:Expression ;
     dc:type <http://books.example.com/product-types/BOOK> . 

<http://books.example.com/products/9780596802189.EBOOK> a frbr:Expression ;
     dc:type <http://books.example.com/product-types/EBOOK> .

<p>
 Both
 <span rdfbase rdfvocab="http://microformats.org/profile/hcard" rdfinclude="home"><span rdfpredicate="fn">Princeton</span></span>
 and
 <span rdfbase rdfvocab="http://microformats.org/profile/hcard" rdfinclude="home"><span rdfpredicate="fn">Trekkie</span></span>
 live at
 <span id="home" rdfpredicate="adr" rdfbase><span rdfpredicate="street-address">Avenue Q</span>.</span>
</p>

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix dct: <http://purl.org/dc/terms/> .
@prefix hcard: <http://www.w3.org/1999/xhtml/RDFa5#http%3A%2F%2Fmicroformats.org%2Fprofile%2Fhcard%23%3A> .

<> <http://www.w3.org/1999/xhtml/RDFa5#item> _:n0 ;
   <http://www.w3.org/1999/xhtml/RDFa5#item> _:n1 .
_:n0 rdf:type <http://microformats.org/profile/hcard> ;
     hcard:fn "Princeton" ;
     hcard:adr _:n2 .
_:n1 rdf:type <http://microformats.org/profile/hcard> ;
     hcard:fn "Trekkie" ;
     hcard:adr _:n2 .
_:n2 hcard:adr%20street-address "Avenue Q" ;
     hcard:adr%20street-address "Avenue Q" .

7 IANA considerations

7.1 application/RDFa5+json

This registration is for community review and will be submitted to the IESG for review, approval, and registration with IANA.

Type name:

application

Subtype name:

RDFa5+json

Required parameters:

Same as for application/json [JSON]

Optional parameters:

Same as for application/json [JSON]

Encoding considerations:

Always UTF-8.

Security considerations:

Same as for application/json [JSON]

Interoperability considerations:

Same as for application/json [JSON]

Published specification:

Labeling a resource with the application/RDFa5+json type asserts that the resource is a JSON text that consists of an object with a single entry called "items" consisting of an array of entries, each of which consists of an object with two entries, one called "type" whose value is an array of strings, and one called "properties" whose value is an object whose entries each have a value consisting of an array of either objects or strings, the objects being of the same form as the objects in the aforementioned "items" entry. As such, the relevant specifications are the JSON specification and this specification. [JSON]

Applications that use this media type:

Same as for application/json [JSON]

Additional information:

Magic number(s):

Same as for application/json [JSON]

File extension(s):

Same as for application/json [JSON]

Macintosh file type code(s):

Same as for application/json [JSON]

Person & email address to contact for further information:

Ian Hickson <ian@hixie.ch>

Intended usage:

Common

Restrictions on usage:

No restrictions apply.

Author:

Ian Hickson <ian@hixie.ch>

Change controller:

W3C and WHATWG

Fragment identifiers used with application/RDFa5+json resources have the same semantics as when used with application/json. [JSON]

References

Status: Implemented and widely deployed

All references are normative unless marked "Non-normative".

[HTML5]

HTML5, I. Hickson, D. Hyatt. W3C.

[JSON]

The application/json Media Type for JavaScript Object Notation (JSON), D. Crockford. IETF.

[RFC2119]

Key words for use in RFCs to Indicate Requirement Levels, S. Bradner. IETF.

[RFC3987]

Internationalized Resource Identifiers (IRIs), M. Dürst, M. Suignard. IETF.

[WEBIDL]

Web IDL, C. McCormack. W3C.

Acknowledgements

For a full list of acknowledgements, please see the HTML5 specification. [HTML5]