Representing Content in RDF

W3C Editor's Draft 14 May 2009

This version:: http://www.w3.org/WAI/ER/Content/WD-Content-in-RDF-20090514/
Latest published version:: http://www.w3.org/TR/Content-in-RDF/
Latest internal version:: http://www.w3.org/WAI/ER/Content-in-RDF/
Previous published version:: http://www.w3.org/TR/2008/WD-Content-in-RDF-20080908/
Previous internal version:: http://www.w3.org/WAI/ER/Content/WD-Content-in-RDF-20081216
Editors:: Johannes Koch, Fraunhofer-Gesellschaft (Fraunhofer Institute for Applied Information Technology FIT); Carlos A Velasco, Fraunhofer-Gesellschaft (Fraunhofer Institute for Applied Information Technology FIT)

Abstract

This document is a specification for a vocabulary to represent Content in 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) 1.0 Schema evaluation report. The document contains introductory information on its usage and some examples.

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/.

@@@ 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 RDF approach 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 it 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
- 1.1 Namespaces
- 1.2 Use Cases
Classes
Properties
Conformance
Usage scenarios
Limitations of the vocabulary

Appendices

A practical example
Terms
Schema in RDF/XML
Mapping between DOM and Content-in-RDF properties
Document Changes
References

1 Introduction

This document is the specification for a vocabulary to represent Content in 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 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.

1.1 Namespaces

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.
`rdf`	`http://www.w3.org/1999/02/22-rdf-syntax-ns#`	Namespace for RDF [RDF].

1.2 Use cases

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 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.

2 Classes

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.

2.1 Content Class

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 (e.g., images or movies), XML files, etc.

There are three subclasses from the Content class: cnt:Base64Content, cnt:TextContent and cnt:XMLContent.

[Editor's note: Should we here suggest a way to connect cnt:TextContent/cnt:XMLContent resources to cnt:Base64Content resources, e.g. via dct:source?]

2.1.1 Base64Content Class

The cnt:Base64Content 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:
- cnt:bytes
- cnt:characterEncoding
Range of: none

Examples

Example 2.1: This example displays the representation of the W3C logo as a Base64Content resource. (Note: due to its length, the encoded string has been chunked until {...}.)

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:cnt="http://www.w3.org/2008/content#">

  <cnt:Base64Content rdf:about="http://www.w3.org/Icons/w3c_home.png">
    <cnt:bytes>77+9UE5HDQoaCgAAAA1JSERSAAAASAAAADAIAwAAAO+{...}</cnt:bytes>
  </cnt:Base64Content>

</rdf:RDF>

2.1.2 TextContent Class

The cnt:TextContent class is a subclass of the cnt:Content class for any type of textual content.

Related Properties

Domain of:
- cnt:chars
- cnt:characterEncoding
Range of: none

Examples

Example 2.2: The following example represents a CSS file as a TextContent resource.

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:cnt="http://www.w3.org/2008/content#">

  <cnt:TextContent 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:TextContent>

</rdf:RDF>

2.1.3 XMLContent Class

[Editor's note: We have to rename the class because the name starts with 'X', 'M', 'L'. Suggested name: WellformedContent]

The cnt:XMLContent class is a subclass of the cnt:Content class only for wellformed XML content.

See the Mapping between DOM and the Content-in-RDF vocabulary.

Examples

Example 2.3: 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 XMLContent resource.

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:cnt="http://www.w3.org/2008/content#">

  <cnt:XMLContent rdf:about="http://example.org/example203.html">
    <cnt:xmlRest 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:xmlRest>
  </cnt:XMLContent>

</rdf:RDF>

For the use of xmlDecl, xmlLeadingMisc and doctypeDecl see Appendix A: A practical example.

2.2 XMLDecl Class

[Editor's note: We have to rename the class because the name starts with 'X', 'M', 'L'. Suggested name: ???]

An XML declaration. This class is normally used in conjunction with the XMLContent class, when the corresponding XML resource contains an XML declaration. The relation is expressed via the xmlDecl property.

Related Properties

Domain of:
Range of:
- cnt:xmlDecl

See the Mapping between DOM and the Content-in-RDF vocabulary.

Examples

Example 2.4: A typical XML declaration:

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>

Can be expressed as the following XMLDecl resource:

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:cnt="http://www.w3.org/2008/content#">

  <cnt:XMLDecl rdf:ID="xmld0">
    <cnt:xmlStandalone>no</cnt:xmlStandalone>
    <cnt:xmlEncoding>UTF-8</cnt:xmlEncoding>
    <cnt:xmlVersion>1.0</cnt:xmlVersion>
  </cnt:XMLDecl>

</rdf:RDF>

2.3 DoctypeDecl Class

A document type declaration. Likewise XMLDecl, this class is normally used in conjunction with the XMLContent class, when the corresponding XML resource contains a document type declaration. The relation is expressed via the doctypeDecl property.

Related Properties

Domain of:
Range of:
- cnt:doctypeDecl

See the Mapping between DOM and the Content-in-RDF vocabulary.

Examples

Example 2.5: 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:

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:cnt="http://www.w3.org/2008/content#">

  <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>

</rdf:RDF>

3 Properties

This section presents a description of the properties of this RDF vocabulary.

3.1 bytes Property

Character string representing the Base64 encoded byte sequence of the given content.

Domain:: cnt:Base64Content
Range:: Literal

3.2 characterEncoding Property

The character encoding.

When used with Base64Content: 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 TextContent: 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 XMLContent: 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

3.3 chars Property

The character sequence of the given content.

Domain:: cnt:TextContent
Range:: Literal

3.4 doctypeDecl Property

This property relates an XML Content to its Document Type Declaration.

Domain:: cnt:XMLContent
Range:: cnt:DoctypeDecl

3.5 doctypeName Property

The document type name.

Domain:: cnt:DoctypeDecl
Range:: Literal

3.6 internalSubset Property

The internal subset of a document type declaration.

Domain:: cnt:DoctypeDecl
Range:: Literal

3.7 publicId Property

The formal public identifier of a document type declaration.

Domain:: cnt:DoctypeDecl
Range:: Literal

3.8 systemId Property

The system identifier of a document type declaration.

Domain:: cnt:DoctypeDecl
Range:: Literal typed xsd:anyURI

[Editor's note: add link to XSD datatypes?]