下面是一小部分
Architecture of the World Wide Web, Volume One
W3C Recommendation 15 December 2004
This version:
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/]http://www.w3.org/TR/2004/REC-webarch-20041215/[/URL]
Latest version:
[URL=http://www.w3.org/TR/webarch/]http://www.w3.org/TR/webarch/[/URL]
Previous version:
[URL=http://www.w3.org/TR/2004/PR-webarch-20041105/]http://www.w3.org/TR/2004/PR-webarch-20041105/[/URL]
Editors:
[URL=http://www.w3.org/People/Jacobs]Ian Jacobs[/URL], W3C
Norman Walsh, Sun Microsystems, Inc.
Authors:
See [URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#acks]acknowledgments (§8)[/URL].
Please refer to the [URL=http://www.w3.org/2001/tag/webarch/errata.html]errata[/URL] for this document, which may include some normative corrections.
See also [URL=http://www.w3.org/2003/03/Translations/byTechnology?technology=webarch]translations[/URL].
[URL=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright]Copyright[/URL] © 2002-2004 W3C ® (MIT, ERCIM, [URL=http://www.keio.ac.jp/]Keio[/URL]), All Rights Reserved. W3C [URL=http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer]liability[/URL], [URL=http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks]trademark[/URL], [URL=http://www.w3.org/Consortium/Legal/copyright-documents]document use[/URL] and [URL=http://www.w3.org/Consortium/Legal/copyright-software]software licensing[/URL] rules apply. Your interactions with this site are in accordance with our [URL=http://www.w3.org/Consortium/Legal/privacy-statement#Public]public[/URL] and [URL=http://www.w3.org/Consortium/Legal/privacy-statement#Members]Member[/URL] privacy statements.
--------------------------------------------------------------------------------
Abstract
The World Wide Web uses relatively simple technologies with sufficient scalability, efficiency and utility that they have resulted in a remarkable information space of interrelated resources, growing across languages, cultures, and media. In an effort to preserve these properties of the information space as the technologies evolve, this architecture document discusses the core design components of the Web. They are identification of resources, representation of resource state, and the protocols that support the interaction between agents and resources in the space. We relate core design components, constraints, and good practices to the principles and properties they support.
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 [URL=http://www.w3.org/TR/]W3C technical reports index[/URL] at http://www.w3.org/TR/.
This is the 15 December 2004 Recommendation of “Architecture of the World Wide Web, Volume One.” This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
This document was developed by W3C's [URL=http://www.w3.org/2001/tag/]Technical Architecture Group (TAG)[/URL], which, by [URL=http://www.w3.org/2001/07/19-tag]charter[/URL] maintains a [URL=http://www.w3.org/2001/tag/issues.html]list of architectural issues[/URL]. The scope of this document is a useful subset of those issues; it is not intended to address all of them. The TAG intends to address the remaining (and future) issues now that Volume One is published as a W3C Recommendation. A complete [URL=http://www.w3.org/2001/tag/webarch/changes.html]history of changes[/URL] so this document is available. Please send comments on this document to public-webarch-comments@w3.org ([URL=http://lists.w3.org/Archives/Public/public-webarch-comments/]public archive of public-webarch-comments[/URL]). TAG technical discussion takes place on www-tag@w3.org ([URL=http://lists.w3.org/Archives/Public/public-webarch-comments/]public archive of www-tag[/URL]).
This document was produced under the [URL=http://www.w3.org/Consortium/Process-20010719/policies#ipr]W3C IPR policy of the July 2001 Process Document[/URL]. The TAG maintains a [URL=http://www.w3.org/2001/tag/disclosures]public list of patent disclosures[/URL] relevant to this document; 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) with respect to this specification should disclose the information in accordance with [URL=http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure]section 6 of the W3C Patent Policy[/URL].
Table of Contents
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#intro]1. Introduction[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#about]1.1. About this Document[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#doc-audience]1.1.1. Audience of this Document[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#doc-scope]1.1.2. Scope of this Document[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#app-principles]1.1.3. Principles, Constraints, and Good Practice Notes[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#identification]2. Identification[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#uri-benefits]2.1. Benefits of URIs[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#id-resources]2.2. URI/Resource Relationships[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#URI-collision]2.2.1. URI collision[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#uri-assignment]2.2.2. URI allocation[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#indirect-identification]2.2.3. Indirect Identification[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#identifiers-comparison]2.3. URI Comparisons[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#uri-aliases]2.3.1. URI aliases[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#representation-reuse]2.3.2. Representation reuse[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#URI-scheme]2.4. URI Schemes[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#URI-registration]2.4.1. URI Scheme Registration[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#uri-opacity]2.5. URI Opacity[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#fragid]2.6. Fragment Identifiers[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#identifiers-future]2.7. Future Directions for Identifiers[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#i18n-id]2.7.1. Internationalized identifiers[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#future-comparison]2.7.2. Assertion that two URIs identify the same resource[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#interaction]3. Interaction[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#dereference-uri]3.1. Using a URI to Access a Resource[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#dereference-details]3.1.1. Details of retrieving a representation[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#internet-media-type]3.2. Representation Types and Internet Media Types[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#media-type-fragid]3.2.1. Representation types and fragment identifier semantics[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#frag-coneg]3.2.2. Fragment identifiers and content negotiation[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#metadata-inconsistencies]3.3. Inconsistencies between Representation Data and Metadata[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#safe-interaction]3.4. Safe Interactions[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#unsafe-accountability]3.4.1. Unsafe interactions and accountability[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#representation-management]3.5. Representation Management[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#URI-persistence]3.5.1. URI persistence[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#id-access]3.5.2. Linking and access control[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#supporting-navigation]3.5.3. Supporting Navigation[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#interaction-future]3.6. Future Directions for Interaction[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#formats]4. Data Formats[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#binary]4.1. Binary and Textual Data Formats[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#ext-version]4.2. Versioning and Extensibility[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#versioning]4.2.1. Versioning[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#versioning-xmlns]4.2.2. Versioning and XML namespace policy[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#extensibility]4.2.3. Extensibility[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#composition]4.2.4. Composition of data formats[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pci]4.3. Separation of Content, Presentation, and Interaction[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#hypertext]4.4. Hypertext[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#uri-refs]4.4.1. URI references[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-formats]4.5. XML-Based Data Formats[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-when]4.5.1. When to use an XML-based format[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-links]4.5.2. Links in XML[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-namespaces]4.5.3. XML namespaces[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#namespace-document]4.5.4. Namespace documents[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-qnames]4.5.5. QNames in XML[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-id-semantics]4.5.6. XML ID semantics[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-media-types]4.5.7. Media types for XML[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#xml-fragids]4.5.8. Fragment identifiers in XML[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#media-types-infospace]4.6. Future Directions for Data Formats[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#general]5. General Architecture Principles[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#orthogonal-specs]5.1. Orthogonal Specifications[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#language-extensibility]5.2. Extensibility[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#error-handling]5.3. Error Handling[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#protocol-interop]5.4. Protocol-based Interoperability[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#index]6. Glossary[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#refs]7. References[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#archspecs]7.1. Architectural Specifications[/URL]
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#acks]8. Acknowledgments[/URL]
List of Principles, Constraints, and Good Practice Notes
The following principles, constraints, and good practice notes are discussed in this document and listed here for convenience. There is also a [URL=http://www.w3.org/TR/2004/REC-webarch-20041215/summary.html]free-standing summary[/URL].
Identification
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-global-id]Global Identifiers[/URL] (principle, 2)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-use-uris]Identify with URIs[/URL] (practice, 2.1)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-uri-collision]URIs Identify a Single Resource[/URL] (constraint, 2.2)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#avoid-uri-aliases]Avoiding URI aliases[/URL] (practice, 2.3.1)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#lc-uri-chars]Consistent URI usage[/URL] (practice, 2.3.1)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-reuse-uri-schemes]Reuse URI schemes[/URL] (practice, 2.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-uri-opacity]URI opacity[/URL] (practice, 2.5)
Interaction
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-reuse-formats]Reuse representation formats[/URL] (practice, 3.2)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-server-auth]Data-metadata inconsistency[/URL] (constraint, 3.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-metadata-association]Metadata association[/URL] (practice, 3.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-deref-safe]Safe retrieval[/URL] (principle, 3.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-describe-resource]Available representation[/URL] (practice, 3.5)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#implied-dereference]Reference does not imply dereference[/URL] (principle, 3.5)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-service-uri]Consistent representation[/URL] (practice, 3.5.1)
Data Formats
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-version-info]Version information[/URL] (practice, 4.2.1)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-doc-ns-policy]Namespace policy[/URL] (practice, 4.2.2)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-allow-exts]Extensibility mechanisms[/URL] (practice, 4.2.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-conform-exts]Extensibility conformance[/URL] (practice, 4.2.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-unknown-extension]Unknown extensions[/URL] (practice, 4.2.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#cpi]Separation of content, presentation, interaction[/URL] (practice, 4.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#link-mechanism]Link identification[/URL] (practice, 4.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#web-linking]Web linking[/URL] (practice, 4.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#generic-uri]Generic URIs[/URL] (practice, 4.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#use-hypertext-links]Hypertext links[/URL] (practice, 4.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#use-namespaces]Namespace adoption[/URL] (practice, 4.5.3)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-namespace-documents]Namespace documents[/URL] (practice, 4.5.4)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#qname-uri-syntax]QNames Indistinguishable from URIs[/URL] (constraint, 4.5.5)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#qname-mapping]QName Mapping[/URL] (practice, 4.5.5)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#no-text-xml]XML and "text/*"[/URL] (practice, 4.5.7)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#no-charset]XML and character encodings[/URL] (practice, 4.5.7)
General Architecture Principles
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#pr-orthogonality]Orthogonality[/URL] (principle, 5.1)
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#no-silent-recovery]Error recovery[/URL] (principle, 5.3)
--------------------------------------------------------------------------------
1. Introduction
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 (URI).
Examples such as the following travel scenario are used throughout this document to illustrate typical behavior of Web agents—people or software acting on this information space. A user agent acts on behalf of a user. Software agents include servers, proxies, spiders, browsers, and multimedia players.
Story
While planning a trip to Mexico, Nadia reads “Oaxaca weather information: 'http://weather.example.com/oaxaca'” in a glossy travel magazine. Nadia has enough experience with the Web to recognize that "http://weather.example.com/oaxaca" is a URI and that she is likely to be able to retrieve associated information with her Web browser. When Nadia enters the URI into her browser:
The browser recognizes that what Nadia typed is a URI.
The browser performs an information retrieval action in accordance with its configured behavior for resources identified via the "http" URI scheme.
The authority responsible for "weather.example.com" provides information in a response to the retrieval request.
The browser interprets the response, identified as XHTML by the server, and performs additional retrieval actions for inline graphics and other content as necessary.
The browser displays the retrieved information, which includes hypertext links to other information. Nadia can follow these hypertext links to retrieve additional information.
This scenario illustrates the three architectural bases of the Web that are discussed in this document:
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#identification]Identification (§2)[/URL]. URIs are used to identify resources. In this travel scenario, the resource is a periodically updated report on the weather in Oaxaca, and the URI is “http://weather.example.com/oaxaca”.
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#interaction]Interaction (§3)[/URL]. Web agents communicate using standardized protocols that enable interaction through the exchange of messages which adhere to a defined syntax and semantics. By entering a URI into a retrieval dialog or selecting a hypertext link, Nadia tells her browser to perform a retrieval action for the resource identified by the URI. In this example, the browser sends an HTTP GET request (part of the HTTP protocol) to the server at "weather.example.com", via TCP/IP port 80, and the server sends back a message containing what it determines to be a representation of the resource as of the time that representation was generated. Note that this example is specific to hypertext browsing of information—other kinds of interaction are possible, both within browsers and through the use of other types of Web agent; our example is intended to illustrate one common interaction, not define the range of possible interactions or limit the ways in which agents might use the Web.
[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#formats]Formats (§4)[/URL]. Most protocols used for representation retrieval and/or submission make use of a sequence of one or more messages, which taken together contain a payload of representation data and metadata, to transfer the representation between agents. The choice of interaction protocol places limits on the formats of representation data and metadata that can be transmitted. HTTP, for example, typically transmits a single octet stream plus metadata, and uses the "Content-Type" and "Content-Encoding" header fields to further identify the format of the representation. In this scenario, the representation transferred is in XHTML, as identified by the "Content-type" HTTP header field containing the registered Internet media type name, "application/xhtml+xml". That Internet media type name indicates that the representation data can be processed according to the XHTML specification.
Nadia's browser is configured and programmed to interpret the receipt of an "application/xhtml+xml" typed representation as an instruction to render the content of that representation according to the XHTML rendering model, including any subsidiary interactions (such as requests for external style sheets or in-line images) called for by the representation. In the scenario, the XHTML representation data received from the initial request instructs Nadia's browser to also retrieve and render in-line the weather maps, each identified by a URI and thus causing an additional retrieval action, resulting in additional representations that are processed by the browser according to their own data formats (e.g., "application/svg+xml" indicates the SVG data format), and this process continues until all of the data formats have been rendered. The result of all of this processing, once the browser has reached an application steady-state that completes Nadia's initial requested action, is commonly referred to as a "Web page".
The following illustration shows the relationship between identifier, resource, and representation.
In the remainder of this document, we highlight important architectural points regarding Web identifiers, protocols, and formats. We also discuss some important [URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#general]general architectural principles (§5)[/URL] and how they apply to the Web.
1.1. About this Document
This document describes the properties we desire of the Web and the design choices that have been made to achieve them. It promotes the reuse of existing standards when suitable, and gives guidance on how to innovate in a manner consistent with Web architecture.
The terms MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY are used in the principles, constraints, and good practice notes in accordance with RFC 2119 [[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#RFC2119]RFC2119[/URL]].
This document does not include conformance provisions for these reasons:
Conforming software is expected to be so diverse that it would not be useful to be able to refer to the class of conforming software agents.
Some of the good practice notes concern people; specifications generally define conformance for software, not people.
We do not believe that the addition of a conformance section is likely to increase the utility of the document.
1.1.1. Audience of this Document
This document is intended to inform discussions about issues of Web architecture. The intended audience for this document includes:
Participants in W3C Activities
Other groups and individuals designing technologies to be integrated into the Web
Implementers of W3C specifications
Web content authors and publishers
Note: This document does not distinguish in any formal way the terms "language" and "format." Context determines which term is used. The phrase "specification designer" encompasses language, format, and protocol designers.
1.1.2. Scope of this Document
This document presents the general architecture of the Web. Other groups inside and outside W3C also address specialized aspects of Web architecture, including accessibility, quality assurance, internationalization, device independence, and Web Services. The section on [URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#archspecs]Architectural Specifications (§7.1)[/URL] includes references to these related specifications.
This document strives for a balance between brevity and precision while including illustrative examples. [URL=http://www.w3.org/2001/tag/findings]TAG findings[/URL] are informational documents that complement the current document by providing more detail about selected topics. This document includes some excerpts from the findings. Since the findings evolve independently, this document 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 [URL=http://www.w3.org/2001/tag/issues.html]TAG issues list[/URL].
Many of the examples in this document that involve human activity suppose the familiar Web interaction model (illustrated at the beginning of the Introduction) where a person follows a link via a user agent, the user agent retrieves and presents data, the user follows another link, etc. This document does not discuss in any detail other interaction models such as voice browsing (see, for example, [[URL=http://www.w3.org/TR/2004/REC-webarch-20041215/#VOICEXML2]VOICEXML2[/URL]]). The choice of interaction model may have an impact on expected agent behavior. For instance, when a graphical user agent running on a laptop computer or hand-held device encounters an error, the user agent can report errors directly to the user through visual and audio cues, and present the user with options for resolving the errors. On the other hand, when someone is browsing the Web through voice input and audio-only output, stopping the dialog to wait for user input may reduce usability since it is so easy to "lose one's place" when browsing with only audio-output. This document does not discuss how the principles, constraints, and good practices identified here apply in all interaction contexts.
1.1.3. Principles, Constraints, and Good Practice Notes
The important points of this document are categorized as follows:
Principle
An architectural principle is a fundamental rule that applies to a large number of situations and variables. Architectural principles include "separation of concerns", "generic interface", "self-descriptive syntax," "visible semantics," "network effect" (Metcalfe's Law), and Amdahl's Law: "The speed of a system is limited by its slowest component."
Constraint
In the design of the Web, some choices, like the names of the p and li elements in HTML, the choice of the colon (:) character in URIs, or grouping bits into eight-bit units (octets), are somewhat arbitrary; if paragraph had been chosen instead of p or asterisk (*) instead of colon, the large-scale result would, most likely, have been the same. This document focuses on more fundamental design choices: design choices that lead to constraints, i.e., restrictions in behavior or interaction within the system. Constraints may be imposed for technical, policy, or other reasons to achieve desirable properties in the system, such as accessibility, global scope, relative ease of evolution, efficiency, and dynamic extensibility.
Good practice
Good practice—by software developers, content authors, site managers, users, and specification designers—increases the value of the Web.
[返回] W3CHINA.ORG讨论区 - 语义网·描述逻辑·本体·RDF·OWL →
W3CHINA.ORG讨论区 - Web新技术讨论 → 『 Web架构 』 → 注意！！Architecture of the World Wide Web, Volume One 成为W3C推荐标准！！
(订阅本版)
2004/12/16 0:55:00
新浪微博
注意！！Architecture of the World Wide Web, Volume One 成为W3C推荐标准！！
