This document is a specification for a vocabulary to represent Content in the Resource Description Framework (RDF). This vocabulary is intended to provide a flexible framework within different usage scenarios to semantically represent any type of content, be it on the Web or in local storage media. For example, it can be used by Web accessibility evaluation tools to record a representation of the assessed Web content in an Evaluation And Report Language (EARL) evaluation report. The document contains introductory information on its usage and some examples.
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/.
@@@ CHANGE @@@This First Public Working Draft of the Representing Content in RDF document was published on 8 September 2008 by the Evaluation and Repair Tools Working Group (ERT WG). It presents an approach using the Resource Description Framework(RDF) for recording different representations of content on the Web or in local storage media. This document is part of the W3C Evaluation And Report Language (EARL). It is expected to be published as a W3C Working Group Note after further review and refinement.
[Editor's note: change text appropriately]
The RDF terms defined by this document can be used to extend the Evaluation And Report Language (EARL) 1.0 Schema, but can also be used separately to record different representations of content for any purpose. For example, if the content is received via the Hypertext Transfer Protocol (HTTP), this vocabulary can be used together with the HTTP Vocabulary in RDF to describe Web content that has been retrieved from a server using specific HTTP headers. The Working Group believes that this document is fairly stable despite being a first public working draft. The group encourages feedback about the approach, as well as about the completeness and maturity of this document by developers and researchers who have interest in representing content in RDF format. Feedback from the W3C Quality Assurance Interest Group, the W3C Semantic Web Interest Group, and the Protocol for Web Description Resources Working Group is particularly welcome. Please send comments on this document by @@@ CHANGE @@@29 September 2008 to the public mailing list of the working group public-wai-ert@w3.org. The archives of the working group mailing list are publicly available.
[Editor's note: change date for comments]
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. The group does not expect this document to become a W3C Recommendation. 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.
- Introduction
- Classes
- Properties
- Conformance
- Usage scenarios
- Limitations of the vocabulary
- A practical example
- Terms
- Mapping between DOM and Content-in-RDF properties
- References
- Document Changes
This document is the specification for a vocabulary to represent Content in the Resource Description Framework (RDF). There is a wide variety of scenarios (see section below) where a representation of any type of content, either on the Web or in any local storage media, is necessary. This specification provides an RDF application that allows to present semantically such content. The vocabulary is built in a flexible manner, thus there are no limitations known at the time of writing this specification. It also provides opportunities for extensions to match particular needs of its users.
This document assumes the following background knowledge:
- Basic knowledge of the Extensible Markup Language (XML) [XML] and its associated technologies.
- Basic knowledge about the Semantic Web and RDF. For references, consult [RDF], [RDF-PRIMER] and [RDFS].
Although the concepts of the Semantic Web are simple, their abstraction with RDF is known to bring difficulties to beginners. It is recommended to read carefully the aforementioned references and other tutorials found on the Web. It must be also borne in mind that RDF is primarily targeted to be machine processable, and therefore, some of its expressions are not very intuitive for developers used to work with XML only. The examples will be serialized using the abbreviated RDF/XML notation.
The keywords must, required, recommended, should, may, and optional are used in accordance with [RFC2119].
For limitations of this vocabulary, see section 5.
Table 1 presents the namespaces typically used by this vocabulary. The core namespace has the URI http://www.w3.org/2008/content# and the prefix cnt. The prefix notation presents the typical conventions used in the Web and in this document to denote a given namespace, and can be freely modified.
Table 1: namespaces used by this document.
| Namespace prefix |
Namespace URI |
Description |
cnt |
http://www.w3.org/2008/content# |
Namespace for Representing Content in RDF. |
dct |
http://purl.org/dc/terms/ |
Namespace for Dublin Core Metadata Terms. |
rdf |
http://www.w3.org/1999/02/22-rdf-syntax-ns# |
Namespace for RDF [RDF]. |
As stated earlier, this framework is designed in an open way to facilitate different implementation scenarios. The origin of the application comes from vocabularies describing testing scenarios like the Evaluation And Report Language (EARL) [EARL]. Typical applications could be:
- Applications dealing with retrieval, editing and storage of content. For example, an archiving application could store in a database annotated media content that includes a serialization of the media files with this vocabulary.
- Applications dealing with the exchange of text documents and other types of media, like Web Services. For example, an AJAX application could exchange document fragments and images with a Web server to react to different user actions.
- Applications dealing with the testing and/or repair of content. For example, an accessibility testing tool could store together with the results of a compliance test, the tested Web resources to ensure that the correct version of the tested subject is available to the developers.
This section presents a description of the classes of this RDF vocabulary. We present every class together with its subclasses. We also include whenever relevant short snippets and examples.
The cnt:Content class is an over arching class for any content that could be found on the Web, in an Intranet or in local storage media, for example. It is recommended always to use one of its subclasses. There is no restriction within the vocabulary scope on what can be represented with this class: textual content, binary files (for example, images or movies), XML files, and so on.
There are three subclasses from the Content class: cnt:ContentAsBase64, cnt:ContentAsText and cnt:ContentAsXML.
In order to connect resources with different cnt:Content sub-types with each other, use the dct:source property to point to the original version. For example, if there is an XML resource transmitted via HTTP, the original version would be a cnt:ContentAsBase64 resource. But cnt:ContentAsText and cnt:ContentAsXML resource could also be created and point to the cnt:ContentAsBase64 resource.
Examples
Example 2.1: This example shows how to relate derived resources to the original resource.
<cnt:ContentAsBase64 rdf:about="http://www.example.org/xml0">
<!-- ... -->
</cnt:ContentAsBase64>
<cnt:ContentAsText rdf:about="http://www.example.org/xml1">
<!-- ... -->
<dct:source rdf:resource="http://www.example.org/xml0"/>
</cnt:ContentAsText>
<cnt:ContentAsXML rdf:about="http://www.example.org/xml2">
<!-- ... -->
<dct:source rdf:resource="http://www.example.org/xml0"/>
</cnt:ContentAsXML>
[Editor's note: The working group asks for comments about this use of dct:source.]
Related Properties
dct:source 
- Points to the original resource.
The cnt:ContentAsBase64 class is a subclass of the cnt:Content class for Base64 encoded binary content (as defined by [RFC2045]) and can be used for any type of content, although its more typical use case is for binary files.
Related Properties
- Domain of:
- Range of: none
Examples
Example 2.2: This example displays the representation of the W3C logo as a ContentAsBase64 resource. (Note: due to its length, the encoded string has been chunked until {...}.)
<cnt:ContentAsBase64 rdf:about="http://www.w3.org/Icons/w3c_home.png">
<cnt:bytes>77+9UE5HDQoaCgAAAA1JSERSAAAASAAAADAIAwAAAO+{...}</cnt:bytes>
</cnt:ContentAsBase64>
The cnt:ContentAsText class is a subclass of the cnt:Content class for any type of textual content.
Related Properties
- Domain of:
- Range of: none
Examples
Example 2.3: The following example represents a Cascading Style Sheet (CSS) file as a ContentAsText resource.
<cnt:ContentAsText rdf:about="http://example.org/example.css">
<cnt:characterEncoding>UTF-8</cnt:characterEncoding>
<cnt:chars>body {
color: #000;
background: #fff
}
h1 {
font-size: 1.6em
}
h2 {
font-size: 1.3em
}</cnt:chars>
</cnt:ContentAsText>
The cnt:ContentAsXML class is a subclass of the cnt:Content class only for wellformed XML content.
Related Properties
- Domain of:
- Range of: none
See the Mapping between the Document Object Model (DOM) and the Content-in-RDF vocabulary.
Examples
Example 2.4: The XHTML page with the following source code:
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title>The title</title>
</head>
<body>
<p>Some paragraph.</p>
</body>
</html>
could be represented as this ContentAsXML resource.
<cnt:ContentAsXML rdf:about="http://example.org/example203.html">
<cnt:rest rdf:parseType="Literal"><html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title>The title</title>
</head>
<body>
<p>Some paragraph.</p>
</body>
</html></cnt:rest>
</cnt:ContentAsXML>
For the use of leadingMisc and dtDecl see Appendix A: A practical example.
A document type declaration. This class is normally used in conjunction with the ContentAsXML class, when the corresponding XML resource contains a document type declaration. The relation is expressed via the dtDecl property.
Related Properties
See the Mapping between the Document Object Model (DOM) and the Content-in-RDF vocabulary.
Examples
Example 2.6: A typical XHTML 1.0 Strict document type declaration:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
could be represented as
the following DoctypeDecl resource:
<cnt:DoctypeDecl rdf:ID="dtd0">
<cnt:doctypeName>html</cnt:doctypeName>
<cnt:publicId>-//W3C//DTD XHTML 1.0 Strict//EN</cnt:publicId>
<cnt:systemId>http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd</cnt:systemId>
</cnt:DoctypeDecl>
This section presents a description of the properties of this RDF vocabulary.
Character string representing the Base64 encoded byte sequence of the given content.
- Domain:
cnt:ContentAsBase64- Range:
- Literal
The character encoding.
When used with ContentAsBase64: If the byte sequence was created from a given character sequence this property can be used to store the character encoding that was applied to create the byte sequence.
When used with ContentAsText: If the character sequence was created from a given byte sequence this property can be used to store the character encoding that was applied to create the character sequence.
When used with ContentAsXML: If the parser's input character stream was created from a given byte stream this property can be used to store the character encoding that was applied to create the character stream. Note: This is the used character encoding, not the one declared in an XML declaration.
- Domain:
cnt:Content- Range:
- Literal
The character sequence of the given content.
- Domain:
cnt:ContentAsText- Range:
- Literal
The character encoding specified in the XML declaration.
- Domain:
cnt:ContentAsXML- Range:
- Literal
The document type name.
- Domain:
cnt:DoctypeDecl- Range:
- Literal
This property relates an XML Content to its Document Type Declaration.
- Domain:
cnt:ContentAsXML- Range:
cnt:DoctypeDecl
The internal subset of a document type declaration.
- Domain:
cnt:DoctypeDecl- Range:
- Literal
The part of the XML information items (whitespace, comments and processing instructions) following the XML declaration and preceding the document type declaration if there is one.
- Domain:
cnt:ContentAsXML- Range:
- XML Literal
The formal public identifier of a document type declaration.
- Domain:
cnt:DoctypeDecl- Range:
- Literal
- The part of the XML information items following the document type declaration if there is a document type declaration, or
- the part following the XML declaration if there is no document type declaration, or
- the whole XML information items if there is neither XML declaration nor document type declaration.
It contains comments, processing instructions and the root element.
- Domain:
cnt:ContentAsXML- Range:
- XML Literal
The standalone document declaration.
- Domain:
cnt:ContentAsXML- Range:
- Literal
The system identifier of a document type declaration.
- Domain:
cnt:DoctypeDecl- Range:
- Literal typed xsd:anyURI
The XML version specified in the XML declaration.
- Domain:
cnt:ContentAsXML- Range:
- Literal
This section describes conformance with this Content-in-RDF specification. It differentiates between the following entities:
[Editor's note: The working group asks for comments about a more colloquial word for "Content-in-RDF Graph".]
- Content-in-RDF Graph
- An individual file or collection of files that contain Content-in-RDF data
- Content-in-RDF Producer
- A software tool or Web-based application that produces Content-in-RDF data
- Content-in-RDF Consumer
- A software tool or Web-based application that processes Content-in-RDF data
Graphs conforming to this Content-in-RDF specification must meet the following requirements:
- A ContentAsBase64 must have exactly one bytes (specified by
cnt:bytes).
- A ContentAsBase64 may have one character encoding (specified by
cnt:characterEncoding).
- A ContentAsText must have exactly one chars (specified by
cnt:chars).
- A ContentAsText may have one character encoding (specified by
cnt:characterEncoding).
- A ContentAsXML must have exactly one XML rest (specified by
cnt:rest).
- A ContentAsXML may have one leadingMisc (specified by
cnt:leadingMisc).
- A ContentAsXML may have one Document type declaration (referenced by
cnt:dtDecl).
- A ContentAsXML may have one character encoding (specified by
cnt:characterEncoding).
- A ContentAsXML must have exactly one XML version (specified by
cnt:version).
- A ContentAsXML may have one XML character encoding (specified by
cnt:declaredEncoding).
- A ContentAsXML may have one XML standalone declaration (specified by
cnt:standalone).
- A DoctypeDecl must have exactly one Document type name (specified by
cnt:doctypeName).
- A DoctypeDecl may have one public identifier (specified by
cnt:publicId).
- A DoctypeDecl may have one system identifier (specified by
cnt:systemId).
- A DoctypeDecl may have one internal subset (specified by
cnt:internalSubset).
Producers conforming to this Content-in-RDF specification must meet the following requirements:
- A Producer must generate conforming graphs.
- A Producer must be able to serialize graphs in RDF/XML serialization [RDF-XML] and should also support other RDF serializations.
- A Producer must generate all of the terms summarized in Appendix B: Terms for which there is information available to it.
Consumers conforming to this Content-in-RDF specification must meet the following requirements:
- A Consumer must process conforming graphs.
- A Consumer must process graphs from any RDF/XML serialization [RDF-XML] and should also support other RDF serializations.
- A Consumer must process all of the terms summarized in Appendix B: Terms for which there is information available to it.
We have identified some situations to make clear when to create which type of content resources. The following are only recommendations and are non-normative:
Situation A: byte sequence of non-text content
This includes images, multimedia, or other non-text resources. The byte sequence is recorded in Base64 format and represented as a literal using the cnt:bytes property of the cnt:ContentAsBase64. Non-text content should not be represented using cnt:ContentAsText.
Situation B: byte sequence of text content with appropriate character encoding information
This includes HTML, CSS, client-side script, or other text-based resources. Given the byte sequence of text content (byteSeq) received from a Web server and an appropriate character encoding (ce). byteSeq is recorded in Base64 format and represented as a literal using the cnt:bytes property of the cnt:ContentAsBase64.
After transforming the byteSeq to a character sequence charSeq using character encoding ce, charSeq is represented as a literal using the cnt:chars property of the cnt:ContentAsText and ce as a literal usind the cnt:characterEncoding property.
Situation C: byte sequence of text content with inappropriate character encoding information
Given the byte sequence of text content (byteSeq) received from a Web server and an inappropriate character encoding (ce). byteSeq is recorded in Base64 format and represented as a literal using the cnt:bytes property of the cnt:ContentAsBase64. Because transforming byteSeq to a character sequence charSeq using character encoding ce fails, no cnt:ContentAsText resource can be created.
Situation D: character sequence of text content with appropriate character encoding information
Given the character sequence of text content (charSeq) created in memory and an appropriate character encoding (ce). A cnt:ContentAsText resource may be created with a cnt:chars property with an object literal created from charSeq. After transforming charSeq to byte sequence byteSeq using character encoding ce, a cnt:ContentAsBase64 resource may be created with cnt:bytes property with an object literal byteSeq and cnt:characterEncoding property with an object literal ce.
Situation E: byte sequence of XML content with appropriate character encoding information
Given the byte sequence of wellformed XML content (byteSeq) received from a Web server and an appropriate character encoding (ce). cnt:ContentAsBase64 and cnt:ContentAsText resources may be created as in situation B. Additionally, an cnt:ContentAsXML resource may be created.
Situation F: Document Object Model (DOM) changed in memory
Given a DOM Document in memory, originally created by parsing some XML source, but afterwards changed by DOM operations. A cnt:XMLDecl resource may be created from the information in the Document node itself (version, declaredEncoding and standalone), and a cnt:DoctypeDecl resource from the information in the DocumentType node. A cnt:ContentAsXML resource may be created after serializing the relevant child nodes of the Document node to create object literals for cnt:leadingMisc (serialize Comment and ProcessingInstruction nodes preceding a DocumentType node) and cnt:rest (serialize nodes following a DocumentType node). See the Mapping between the Document Object Model (DOM) and Content-in-RDF properties.
The vocabulary provides a framework that allows the representation of any type of content. Of course, there are many possibilities for extensions that will allow the inclusion of additional metadata, like, for example, that included in some multimedia formats. Typical scenarios for extensions could be:
- Classes to specify the Document Object Model (DOM) of XML or HTML documents.
- Classes to specify the metadata of multimedia content like audio or image files.
- Properties to ensure the integrity of data by providing some kind of checksum algorithm.
However, at the point of writing this specification, the Working Group has decided to provide the basic framework that will support the immediate needs of vocabularies using this specification like the Evaluation and Report Language (EARL) [EARL], leaving the room open for further extensions as new use cases are presented to us.
To understand the versatility of the vocabulary, let us assume we have a given XHTML page containing an XML declaration, a comment preceding a document type declaration and some XHTML elements.
Example 2.6: A typical XHTML page.
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!-- this is a comment -->
<!DOCTYPE html "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
<title>The title</title>
</head>
<body>
<p>Some paragraph.</p>
</body>
</html>
This page could be represented as simple ContentAsText:
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:cnt="http://www.w3.org/2008/content#">
<cnt:ContentAsText rdf:about="http://example.org/example207.html">
<cnt:chars><?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!-- this is a comment -->
<!DOCTYPE html "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>The title</title>
</head>
<body>
<p>Some paragraph.</p>
</body>
</html></cnt:chars>
</cnt:ContentAsText>
</rdf:RDF>
or likewise as ContentAsXML. As the comment <!-- this is a comment --> precedes the document type declaration a cnt:leadingMisc property is created with its object literal containing the comment. The document type declaration is modelled as a DoctypeDecl resource and refered to from the cnt:ContentAsXML resource by the cnt:dtDecl property.
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:cnt="http://www.w3.org/2008/content#"
xml:base="http://example.org/example208.html">
<cnt:DoctypeDecl rdf:ID="dtd0">
<cnt:systemId>http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd</cnt:systemId>
<cnt:publicId>-//W3C//DTD XHTML 1.0 Strict//EN</cnt:publicId>
<cnt:doctypeName>html</cnt:doctypeName>
</cnt:DoctypeDecl>
<cnt:ContentAsXML rdf:about="#">
<cnt:version>1.0</cnt:version>
<cnt:declaredEncoding>UTF-8</cnt:declaredEncoding>
<cnt:standalone>no</cnt:standalone>
<cnt:leadingMisc rdf:parseType="Literal"><!-- this is a comment --></cnt:leadingMisc>
<cnt:dtDecl rdf:resource="#dtd0" />
<cnt:rest rdf:parseType="Literal"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>The title</title>
</head>
<body>
<p>Some paragraph.</p>
</body>
</html></cnt:rest>
</cnt:ContentAsXML>
</rdf:RDF>
The following terms are defined by this specification:
Classes in the Content-in-RDF namespace
| Class name |
Label |
Comment |
Refinements |
Related properties |
cnt:Content |
Content |
The content. |
cnt:ContentAsBase64, cnt:ContentAsText, cnt:ContentAsXML |
|
cnt:ContentAsBase64 |
Base64 Content |
The base64 encoded content (can be used for binary content). |
- |
cnt:bytes, cnt:characterEncoding |
cnt:ContentAsText |
Text Content |
The text content (can be used for text content). |
- |
cnt:chars, cnt:characterEncoding |
cnt:ContentAsXML |
XML content |
The XML content (can be used for XML-wellformed content). |
- |
cnt:version, cnt:declaredEncoding, cnt:standalone, cnt:leadingMisc, cnt:dtDecl, cnt:rest, cnt:characterEncoding |
cnt:DoctypeDecl |
Document type declaration |
The document type declaration. |
- |
cnt:doctypeName, cnt:internalSubset, cnt:publicId, cnt:systemId |
| DOM property |
Content-in-RDF property |
Document.xmlVersion |
version |
Document.xmlEncoding |
declaredEncoding |
Document.xmlStandalone |
standalone |
Document.doctype |
dtDecl |
DocumentType.name |
doctypeName |
DocumentType.publicId |
publicId |
DocumentType.systemId |
systemId |
DocumentType.internalSubset |
internalSubset |
- [EARL]
- Evaluation and Report Language (EARL) 1.0 Schema. W3C Working Draft 28 April 2009.
http://www.w3.org/TR/EARL10/
- [OWL]
- OWL Web Ontology Language Overview. W3C Recommendation 10 February 2004.
http://www.w3.org/TR/owl-features/
- [RDF]
- Resource Description Framework (RDF) Model and Syntax Specification. W3C Recommendation, 22 February 1999.
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/
- [RDF-PRIMER]
- RDF Primer. W3C Recommendation, 10 February 2004.
http://www.w3.org/TR/rdf-primer/
- [RDFS]
- RDF Vocabulary Description Language 1.0: RDF Schema. W3C Recommendation 10 February 2004.
http://www.w3.org/TR/rdf-schema/
- [RDF-XML]
- RDF/XML Syntax Specification (Revised). W3C Recommendation 10 February 2004.
http://www.w3.org/TR/rdf-syntax-grammar/
- [RFC2119]
- Request for Comments: 2119. Key words for use in RFCs to Indicate Requirement Levels, March 1997 (IETF).
http://www.ietf.org/rfc/rfc2119.txt
- [RFC2045]
- Request for Comments: 2045. Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, November 1996 (IETF).
http://www.ietf.org/rfc/rfc2045.txt
- [XML]
- Extensible Markup Language (XML) 1.0 (Fifth Edition). W3C Recommendation 26 November 2008.
http://www.w3.org/TR/xml/
The following is a list of substantial changes since the 8 September 2008 Working Draft:
- due to name restrictions imposed by the XML specification, some class and property names were changed:
XMLContent (now ContentAsXML), xmlEncoding (now declaredEncoding), xmlLeadingMisc (now leadingMisc), xmlRest (now rest), xmlStandalone (now standalone), xmlVersion (now version); Base64Content (now ContentAsBase64), TextContent (now ContentAsText);
- one properties was renamed because its name differed from a class name only by case:
doctypeDecl (now dtDecl);
- the
XMLDecl class was dropped; the domains of properties with domain XMLDecl were changed to ContentAsXML;
- a section about conformance was added.