The identification of resources on the Web by a Uniform Resource Identifier
(URI) alone may not be sufficient, as other factors such as
HTTP content
negotiation might come into play. This issue is particularly significant for
quality assurance testing, conformance claims, and reporting languages like the
W3C Evaluation And Report Language
(EARL). This document provides a representation of the
HTTP vocabulary in the Resource Description Framework
(RDF), to allow quality assurance tools to record the
HTTP headers that have been exchanged between a client and a
server. The RDF terms defined by this document represent the
core HTTP specification defined by RFC 2616, as well as additional
HTTP headers registered by the Internet Assigned Numbers
Authority (IANA). These terms can also be used to record
HTTPS
exchanges.
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 https://www.w3.org/TR/.
HTTP Vocabulary in RDF 1.0 is a supporting document for the Evaluation and Report Language (EARL) 1.0 Schema but can be used in other contexts too. It is considered to be complete and mature but at this time there are not sufficient implementations to finalize this work.
Publication as a Working Group Note 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 defines a representation of the Hypertext Transfer Protocol
(HTTP) using the Resource Description Framework
(RDF). It defines a collection of RDF
classes and properties that represent the HTTP vocabulary as
defined by the HTTP specification [RFC2616]. These RDF terms can be
used to record HTTP or secure HTTP
request and response messages in RDF format, such as by
automated Web accessibility evaluation tools that want to describe Web
resources, including the various headers exchanged between the client and
server during content negotiation. More usage examples for these terms are
described in section 1.2 Use Cases.
Note: The version 1.0 specifies the version of the
HTTP Vocabulary in RDF document and
not the version of HTTP. The vocabulary
defined in this specification is usable for HTTP versions up
to 1.1.
This document is not intended to be a clarification or extension of the
different concepts of the HTTP specification. The
HTTP specification is defined by a series of Request for
Comments (RFC) publications and other documentation,
including [RFC 2616] and [RFC
4229]. These are listed in Appendix C:
References.
Additionally 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], [RDFS], [RDF-PRIMER] and
[OWL].
By default, the vocabulary introduced by this document uses names starting
with upper-case letters for classes and names starting with lower-case letters
for properties. The keywords must, required,
recommended, should, may,
and optional are used in accordance with [RFC2119].
The RDF
representation of the HTTP vocabulary defined by this
document uses the namespace http://www.w3.org/2011/http#. The
prefix http is used throughout this document to denote this
namespace. Table 1 presents the namespaces used by this
document. 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 2 presents additional
RDF data used by this document.
Table 1: namespaces used by this document.
Namespace prefix
Namespace URI
Description
http
http://www.w3.org/2011/http#
Namespace for the core terms of HTTP vocabulary in
RDF.
cnt
http://www.w3.org/2011/content#
Namespace for Representing Content in RDF [Content-in-RDF].
When Web resources are tested, for example for accessibility or other
quality assurance testing, it may be significant to record the exact
headers exchanged between the server and the client during the testing.
Without a record of the exchanged headers, it may not be possible to
re-identify the exact resource (or representation of the resource) that
has been tested. The terms provided by this document allow quality
assurance tools to record the HTTP exchange between a
client and a server, for example to record the POST parameters or the
headers used during content negotiation. The terms provided by this
document can be used in combination with the W3C Evaluation And Report
Language (EARL) [EARL].
Conformance claims that are made about a Web resource or group of Web
resource, are sometimes only applicable under certain constraints. For
example, conformance of a Web site to the W3C Web Content Accessibility
Guidelines (WCAG) [WCAG], may
only be applicable for a certain language of the Web site that is using
language negotiation. When providing machine-readable conformance claims,
for example using the W3C Protocol for Describing Web Resources (POWDER):
Description Resources [POWDER-DR], it is
important to precise any such constraints that may apply.
Web applications using client-side scripting such as AJAX may exchange
additional HTTP messages with the server without using
a different URI. In order to debug such Web
applications, it must be possible to reconstruct the exact history of the
states through which the Web application passed. Web authoring tools that
are designed to develop and debug Web applications could use the terms
provided by this document to record the exact HTTP
messages exchanged between a client and a server. This information could
be provided to the developer as a log to help debug errors in the Web
application.
When indexing RDF information resources that are
available through the HTTP protocol (also called
"scuttering" in Semantic Web parlance), it is often useful to record
information about the HTTP request and response
messages that were exchanged, along with the data for later use. In some
instances, different representations of the RDF
information may be retrieved from the server depending on the
HTTP headers and parameters exchanged. The terms
provided by this document can be used to supplement the collected data
with the HTTP messages as part of a comprehensive
indexing repository.
There are also notable schema limitations in regard to security and privacy
since the content recorded by this vocabulary could potentially contain
sensitive information, for example authentication information in HTTP headers or other
information (login user name, passwords, and so on) within the body of the
message. Since the schema of this document is limited to terms defined by the
HTTP vocabulary, security and privacy considerations need to
be made at the application level. For example, certain parts of the data may be
restricted to appropriate user permissions or obfuscated.
The HTTP 1.1
specification defines eight methods: OPTIONS, GET, HEAD, POST, PUT, DELETE,
TRACE, CONNECT. Additionally [RFC5789] defines the
PATCH method. The RDF
graph available in RDF/XML at http://www.w3.org/2011/http-methods
provides http:Method resources for each of these to be used as
objects for the http:mthd property. A
resource of type http:Method represents the name of a method used
with HTTP.
[HTTP Status Codes] is a registry for status
codes too be used in HTTP. The RDF graph available in
RDF/XML at http://www.w3.org/2011/http-statusCodes
provides http:StatusCode resources for each of these to be used as
objects for the http:sc property. A
resource of type http:StatusCode represents a status code.
Header names to be used in HTTP are registered by the
IANA (see [RFC4229], [Permanent
Headers], and [Provisional Headers]). The
RDF graph available
in RDF/XML at http://www.w3.org/2011/http-headers
provides http:HeaderName resources for each of these to be used as
objects for the http:hdrName
property. A resource of type http:HeaderName represents the name
of a header used with HTTP.
This property relates a resource object of the type Message to
a resource object of the type cnt:Content or a subclass thereof to
be the Message's entity body as defined in [RFC2616]. HTTP bodies are series of bytes.
Thus for the resource object, it is appropriate to point to a
cnt:ContentAsBase64 resource (see [Content-in-RDF] for more information on content
representations using the Resource Desription Framework
(RDF)).
A client sends two requests to a server at www.example.org port
80 via HTTP 1.1 GET. With each request, it sends request
headers. The first request is for a resource in the document root
(/), the second for a resource at /image. While
handling the second request the server performs content negotiation respecting
the request's Accept header and so sends a PNG image. This is indicated by the
response's Vary header.