W3C's Technical Architecture Group (TAG) has released a Last Call Working Draft for the Architecture of the World Wide Web, First Edition. The Working Draft is edited by Ian Jacobs, with contributions from Tim Berners-Lee, Tim Bray, Dan Connolly, Paul Cotton, Roy Fielding, Chris Lilley, David Orchard, Norman Walsh, and Stuart Williams. The document "is written for Web developers, implementers, content authors and publishers. It describes the properties that are desired of the Web and the design choices that have been made to achieve them. The architecture document promotes re-use of existing standards when suitable, and gives guidance on how to innovate in a manner consistent with the Web architecture." Three architectural bases of the Web are discussed: Identification (resources identified by URI), Interaction (protocols defining the syntax and semantics of messages exchanged by agents over a network; web agents communicating information about the state of a resource through the exchange of representations), and Formats (representations built from a non-exclusive set of data formats, used separately or in combination)." Public review and comment on the Working Draft are invited through the last call period ending March 05, 2004.

Bibliographic Information

Architecture of the World Wide Web, First Edition. W3C Working Draft 9-December-2003. Edited by Ian Jacobs (W3C). Version URL: http://www.w3.org/TR/2003/WD-webarch-20031209/. Latest version URL: http://www.w3.org/TR/webarch/. Previous version URL: http://www.w3.org/TR/2003/WD-webarch-20031001/. The document was authored by the W3C Technical Architecture Group which included the following participants: Tim Berners-Lee (co-Chair, W3C), Tim Bray (Antarctica Systems), Dan Connolly (W3C), Paul Cotton (Microsoft Corporation), Roy Fielding (Day Software), Chris Lilley (W3C), David Orchard (BEA Systems), Norman Walsh (Sun), and Stuart Williams (co-Chair, Hewlett-Packard).

Table of Contents:

• 1. Introduction
  • 1.1. About this Document
  • 1.2. General Architecture Principles
• 2. Identification
  • 2.1. URI Comparisons
  • 2.2. URI Ownership
  • 2.3. URI Ambiguity
  • 2.4. URI Schemes
  • 2.5. URI Opacity
  • 2.6. Fragment Identifiers
  • 2.7. Future Directions for Identifiers
• 3. Interaction
  • 3.1. Using a URI to Access a Resource
  • 3.2. Messages and Representations
  • 3.3. Internet Media Type
  • 3.4. Authoritative Representation Metadata
  • 3.5. Safe Interactions
  • 3.6. Representation Management
  • 3.7. Future Directions for Interaction
• 4. Data Formats
  • 4.1. Binary and Textual Data Formats
  • 4.2. Versioning and Extensibility
  • 4.3. Separation of Content, Presentation, and Interaction
  • 4.4. Hypertext
  • 4.5. XML-Based Data Formats
• 5. Term Index
• 6. References
  • 6.1. Internet Specifications
  • 6.2. Architectural Specifications
  • 6.3. Additional References
• 7. Acknowledgments

Web Architecture Document Overview

"The World Wide Web is a network-spanning information space of resources interconnected by links. This information space is the basis of, and is shared by, a number of information systems. Within each of these systems, agents (people and software) retrieve, create, display, analyze, and reason about resources.

Web architecture includes the definition of the information space in terms of identification and representation of its contents, and of the protocols that support the interaction of agents in an information system making use of the space. Web architecture is influenced by social requirements and software engineering principles, leading to design choices that constrain the behavior of systems using the Web in order to achieve desired properties of the shared information space: efficiency, scalability, and the potential for indefinite growth across languages, cultures, and media. This document reflects the three bases of Web architecture: identification, interaction, and representation.

This document presents the general architecture of the Web. Other groups inside and outside W3C also address specialized aspects of Web architecture, including accessibility, internationalization, device independence, and Web Services. The section on Architectural Specifications includes references.

This document strikes a balance between brevity and precision while including illustrative examples. TAG findings are informational documents that complement the current document by providing more detail about selected topics. This document includes some important material from the findings. Since the findings evolve independently, this document also includes references to approved TAG findings. For other TAG issues covered by this document but without an approved finding, references are to entries in the TAG issues list..." [from the Abstract and Scope Statement]

Three Architectural Bases of the Web

"The World Wide Web (WWW, or simply Web) is an information space in which the items of interest, referred to as resources, are identified by global identifiers called Uniform Resource Identifiers (URIs). A travel scenario is used throughout the document to illustrate typical behavior of Web agents -- people or software (on behalf of a person, entity, or process) acting on this information space. Software agents include servers, proxies, spiders, browsers, and multimedia players."

The draft Architecture of the World Wide Web, First Edition document discusses "three architectural bases of the Web:

• Identification. Each resource is identified by a URI. In this travel scenario [presented in the WD], the resource is about the weather in Oaxaca and the URI is 'http://weather.example.com/oaxaca'.

• Interaction. Protocols define the syntax and semantics of messages exchanged by agents over a network. Web agents communicate information about the state of a resource through the exchange of representations. In the travel scenario [presented in the WD], Nadia (by clicking on a hypertext link) tells her browser to request a representation of the resource identified by the URI in the hypertext link. The browser sends an HTTP GET request to the server at 'weather.example.com'. The server responds with a representation that includes XHTML data and the Internet Media Type 'application/xml+xhtml'.

• Formats. Representations are built from a non-exclusive set of data formats, used separately or in combination (including XHTML, CSS, PNG, XLink, RDF/XML, SVG, and SMIL animation). In this [travel] scenario, the representation data is XHTML. While interpreting the XHTML representation data, the browser retrieves and displays weather maps identified by URIs within the XHTML..." [from the Introduction]