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.
If you wish to make comments regarding this HTTP Vocabulary in RDF 1.0 document, please send them to [email protected] (publicly visible mailing list archive).
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 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.
