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<div class="head">
<p><a href="http://www.w3.org/"><img alt="W3C" height="48"
src="http://www.w3.org/Icons/w3c_home" width="72" /></a></p>
<h1><a id="title" name="title" />Content Transformation Landscape 1.0</h1>
<h2><a id="w3c-doctype" name="w3c-doctype" />W3C Working Group Note 27 October 2009</h2>
<dl>
<dt>This version:</dt>
<dd>
<a href="http://www.w3.org/TR/2009/NOTE-ct-landscape-20091027/">http://www.w3.org/TR/2009/NOTE-ct-landscape-20091027/</a>
</dd>
<dt>Latest version:</dt>
<dd>
<a href="http://www.w3.org/TR/ct-landscape/">http://www.w3.org/TR/ct-landscape/</a>
</dd>
<dt>Previous version:</dt>
<dd>
<a href="http://www.w3.org/TR/2007/WD-ct-landscape-20071025/">http://www.w3.org/TR/2007/WD-ct-landscape-20071025/</a>
</dd>
<dt>Editors:</dt>
<dd>Jo Rabin, dotMobi</dd>
<dd>Andrew Swainston [Initial Draft], Vodafone UK</dd>
</dl>
<p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
>Copyright</a> © 2009 <a href="http://www.w3.org/"><acronym
title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology"
>MIT</acronym></a>, <a href="http://www.ercim.org/"><acronym
title="European Research Consortium for Informatics and Mathematics"
>ERCIM</acronym></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules
apply.</p>
</div>
<hr />
<div><h2><a id="abstract" name="abstract" />Abstract</h2><p>This document identifies the issues
surrounding use of transforming proxies in the delivery of Web content. It does not comment
on the techniques that cause these issues, it merely identifies them in order to inform the
requirements of the Content Transformation Guidelines document. That document is to offer
recommendations as to how components of the delivery context can cooperate to achieve, at a
minimum, a functional user experience.</p><p>In this revision the document is largely
historical - the Content Transformation Guidelines document, published under the title
<a href="http://www.w3.org/TR/ct-guidelines/">"Guidelines for Web Content Transformation Proxies"</a> was initially inspired by the set
of requirements identified in this document, but has subsequently evolved based on
available technologies and feedback.</p></div>
<div>
<h2><a id="status" name="status" />Status of this Document</h2>
<p>
<em>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 <a href="http://www.w3.org/TR/">W3C
technical reports index</a> at http://www.w3.org/TR/.</em></p>
<p>This document was produced by the <a
href="http://www.w3.org/2005/MWI/BPWG/Group/TaskForces/CT/">Content Transformation Task
Force</a> of the <a href="http://www.w3.org/2005/MWI/BPWG/">Mobile Web Best Practices
Working Group</a> as part of the <a href="http://www.w3.org/2005/MWI/Activity">Mobile Web
Initiative</a>. It is the <em>Problem Statement</em> referred to in the <a
href="http://www.w3.org/2005/MWI/BPWG/Group/TaskForces/CT/#charter">Charter</a> of the W3C
Mobile Web Initiative Best Practices Working Group <a
href="http://www.w3.org/2005/MWI/BPWG/Group/TaskForces/CT/">Content Transformation Task
Force</a>, and served as a basis for the work on the <a
href="http://www.w3.org/TR/ct-guidelines/">Guidelines for Web Content Transformation Proxies</a>.</p>
<p>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.</p>
<p>Changes since publication of the previous <a href="http://www.w3.org/TR/2007/WD-ct-landscape-20071025/">Working Draft</a> (published on 25 October 2007) are an update of the <a href="#abstract">Abstract</a> section to clarify the historical status of this work and refer to the normative <a href="http://www.w3.org/TR/ct-guidelines/">Guidelines for Web Content Transformation Proxies</a> document that was initially inspired by this document. The Working Group does not anticipate any further change on this document.</p>
<p>Comments on this document may be sent to the Working Group's public email list <a href="mailto:public-bpwg-comments@w3.org">public-bpwg-comments@w3.org</a>, a <a href="http://lists.w3.org/Archives/Public/public-bpwg-comments/">publicly archived mailing list</a>. The Working Group rather expects comments to be made against the normative <a href="http://www.w3.org/TR/ct-guidelines/">Guidelines for Web Content Transformation Proxies</a> document.</p>
<p> This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/37584/status">public list of any patent disclosures</a> 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 <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>
</div>
<div class="toc">
<h2><a id="contents" name="contents" />Table of Contents</h2>
<p class="toc">1 <a href="#introduction">Introduction</a><br /> 1.1 <a href="#d0e113"
>Purpose</a><br /> 1.2 <a href="#d0e121">Scope</a><br /> 1.3 <a
href="#d0e128">Structure of the Document</a><br /> 2 <a href="#landscape">Landscape</a><br
/> 2.1 <a href="#d0e144">Accessing Web Content from Mobile Devices</a><br />
2.2 <a href="#d0e182">Content Transformation Proxies</a><br /> 2.2.1
<a href="#d0e211">Advantages of Content Transformation</a><br /> 2.2.2 <a
href="#d0e224">Issues with Content Transformation</a><br />
2.2.2.1 <a href="#d0e227">Web Presentation</a><br />
2.2.2.2 <a href="#d0e248">Non Web Applications</a><br />
2.2.2.3 <a href="#d0e276">Legal, Moral and Commercial Issues</a><br
/> 2.2.2.4 <a href="#d0e292">Security Issues</a><br /> 3 <a
href="#constraints">Constraints</a><br /></p>
<h3><a id="appendices" name="appendices" />Appendices</h3>
<p class="toc">A <a href="#terminologyNote">Terminology</a> (Non-Normative)<br /> B <a
href="#d0e364">References</a> (Non-Normative)<br /> C <a href="#d0e374"
>Acknowledgments</a> (Non-Normative)<br /></p>
</div>
<hr />
<div class="body">
<div class="div1">
<h2><a id="introduction" name="introduction" />1 Introduction</h2>
<p>Mobile Web Best Practices <a href="#BestPractices">[BestPractices]</a> encourages content
providers to produce "made for mobile" experiences of their Web sites. While the number of
such Web sites continues to increase, there are still many Web sites that are unaware of
mobile presentation. Those Web sites, when accessed from mobile devices, do not present a
satisfactory user experience or may indeed cause failure of the user's device. In order to
mitigate this unsatisfactory experience, mobile network operators and others use proxies
to transform the content of these sites.</p>
<p>At the same time there are an increasing number of highly capable mobile devices that
offer enhanced browsing experiences designed to assist users of mobile devices with their
typically small screen and limited input capabilities to navigate sites designed with
larger displays, pointing devices and full keyboards in mind.</p>
<p>The W3C MWI <a href="http://www.w3.org/2005/MWI/BPWG/">Best Practices Working Group</a>
recognizes that on the one hand transforming proxies can diminish the value of sites that
have been designed specifically for mobile presentation. On the other hand transforming
proxies can enhance the mobile experience of sites unaware of mobile presentation. Yet
again, transforming proxies can diminish the value of such sites when presented on devices
that are capable of simulating a desktop experience while mobile.</p>
<div class="div2">
<h3><a id="d0e113" name="d0e113" />1.1 Purpose</h3>
<p>This document identifies specific issues that can result from content transformation
and identifies requirements that must be fulfilled by the Content Transformation
Guidelines document. That document identifies techniques that are designed to help
components in the Delivery Context cooperate in the presentation of Web sites in order
that users experience, at a minimum, a <a
href="http://www.w3.org/TR/2005/WD-di-gloss-20050118/#def-functional-user-experience"
>functional user experience</a> and that authors' intentions are fulfilled to whatever
degree possible.</p>
</div>
<div class="div2">
<h3><a id="d0e121" name="d0e121" />1.2 Scope</h3>
<p>While the Working Group's charter refers specifically to mobile, the Working Group
recognizes that the issues here relate to any non-desktop presentation of content, or
indeed presentation of any content that has alternative representations. Hence, in the
following, requirements are presented in a more general form.</p>
<p>This document does not offer comment on the rights and wrongs of any particular issues
it mentions. It does not condone nor deprecate any particular technique. They are
mentioned in order to clarify the requirements of the Guidelines document that
consequently addresses the issues mentioned.</p>
</div>
<div class="div2">
<h3><a id="d0e128" name="d0e128" />1.3 Structure of the Document</h3>
<p>In <a href="#landscape"><b>2 Landscape</b></a> the document identifies specific
benefits and issues relating to content transformation. Where requirements can be
inferred from the discussion they are identified in the text, thus:</p>
<p class="requirement">This is a requirement.</p>
<p>Various technologies and techniques that must be taken into account when satisfying the
requirements are identified in <a href="#constraints"><b>3 Constraints</b></a>.</p>
</div>
</div>
<div class="div1">
<h2><a id="landscape" name="landscape" />2 Landscape</h2>
<div class="div2">
<h3><a id="d0e144" name="d0e144" />2.1 Accessing Web Content from Mobile Devices</h3>
<p>While an increasing number of Web sites [<a id="mobileAware" name="mobileAware"
title="Mobile Aware">Definition</a>: mobile aware] are being designed specifically to
tailor their presentation to be suitable for users in a mobile context (see <a
href="#BestPractices">[BestPractices]</a>), many Web sites [<a id="mobileUnaware"
name="mobileUnaware" title="Mobile Unaware">Definition</a>: mobile unaware] have been
(and continue to be) designed with only the features of desktop browsers in mind. From a
mobile perspective, typical issues with the resulting Web pages are:</p>
<ul>
<li>
<p>page layouts assume a screen larger than the device supports;</p>
</li>
<li>
<p>pages require more memory than the device supports;</p>
</li>
<li>
<p>the design of interaction with the page assumes that a full qwerty keyboard and
mouse are available;</p>
</li>
<li>
<p>pages use content types that the device does not support.</p>
</li>
</ul>
<p>As a result accessing such a Web page from a mobile device often results in a poor or
unusable experience (The differences between desktop and mobile presentation are
discussed in more detail in <a href="#BestPractices">[BestPractices]</a> - <a
href="http://www.w3.org/TR/mobile-bp/#requirements">2 Requirements</a>).</p>
<p>Some Web sites [<a id="mobileBlocking" name="mobileBlocking" title="mobile blocking"
>Definition</a>: mobile blocking], aware that access is not from the expected desktop
context, send either an HTTP error status code or an HTTP success code accompanied by
text indicating that they cannot present an acceptable experience for the user - thus
preventing access from mobile users.</p>
</div>
<div class="div2">
<h3><a id="d0e182" name="d0e182" />2.2 Content Transformation Proxies</h3>
<p>Mobile operators, search engines and others recognize that while the number of mobile
friendly Web sites is growing, there will remain a considerable number of mobile unaware
and mobile blocking sites. One approach to providing a more satisfactory mobile user
experience of mobile unaware and blocking sites is to insert an intermediary in the
communications path between the user agent and the origin server. These intermediaries,
known as [<a id="ctf" name="ctf" title="content transformation proxy">Definition</a>:
content transformation proxies] (see <a href="#terminologyNote"><b>A
Terminology</b></a>) adjust HTML pages designed for desktop presentation to provide an
enhanced user experience when accessed from a mobile device.</p>
<p>In order to avoid blocking behavior and in order to achieve a consistent presentation
from Web sites that vary their experience according to the browser type, proxies
typically work by masquerading as a specific desktop browser, fetching content and then
modifying it before returning it to mobile devices. These transformations include:</p>
<ul>
<li>
<p>character encoding corrections,</p>
</li>
<li>
<p>image reformatting and resizing, </p>
</li>
<li>
<p>layout modifications and page segmentation, </p>
</li>
<li>
<p>multi step JavaScript transaction emulation.</p>
</li>
</ul>
<p>Content transformation proxies can also add content to, or remove it from a page.</p>
<p class="requirement" id="req1">1. It must be possible to make a distinction between
different types of transformation - e.g. correction of malformed markup as opposed to
pagination and addition of headers and footers.</p>
<div class="div3">
<h4><a id="d0e211" name="d0e211" />2.2.1 Advantages of Content Transformation</h4>
<p>The principal advantage of Content Transformation is that it provides the ability for
mobile users to enjoy a Web experience even though a large number of Web sites that
are mobile unaware or mobile blocking.</p>
<p class="requirement" id="req2">2. Transforming proxies must be able to overcome the
behavior of "blocking" sites.</p>
<p>Content transformation also offers opportunities to site designers, allowing their
sites to be served to a wide range or devices while freeing them from having to detect
and keep up to date with the capabilities of new devices.</p>
<p class="requirement" id="req3">3. Transforming proxies must be able to identify their
presence and advertise their capabilities.</p>
<p class="requirement" id="req4">4. Origin servers must be able to selectively enable or
disable features of transforming proxies.</p>
</div>
<div class="div3">
<h4><a id="d0e224" name="d0e224" />2.2.2 Issues with Content Transformation</h4>
<div class="div4">
<h5><a id="d0e227" name="d0e227" />2.2.2.1 Web Presentation</h5>
<p>By presenting requests as though they came from a different device, Content
Transformation prevents mobile aware sites from detecting the actual mobile devices
behind the request. As a result, mobile aware sites whose purpose is to provide
mobile compatible pages or mobile compatible content like ring-tones or Java
applications are unable to operate correctly. Such sites require information about
the actual device.</p>
<p class="requirement" id="req5">5. Origin servers and proxies must be able to
identify the actual identity of components of the delivery context, including
(other) proxies and browsers.</p>
<p>When mobile aware sites send content to devices, they often choose to deliver very
specific variations on their content tailored exactly for the device. Any attempt by
a content transformation proxy to change the content may very well destroy or in any
case decrease the value of the content. For example, a site which delivers ring
tones or wallpaper which it tailors exactly to devices' characteristics may be
rendered useless if the audio format is changed, or less valuable if the color depth
of an image is reduced to something below that which the device is capable of
rendering.</p>
<p class="requirement" id="req6">6. Origin servers must be able to prohibit any kind
of transformation of its content.</p>
<p class="requirement" id="req9">7. Origin servers must be able to advertise author
preferences.</p>
<p>Some Web sites cater for both desktop browsers and mobile devices, especially when
the site recognizes that the device has a browser that is capable of providing a
'full screen' presentation mode. In these cases the user of the mobile device may be
prevented from exercising their choice of presentation and may be unable to access
either the site's mobile or desktop presentation in its original form.</p>
<p class="requirement" id="req7">8. Browsers must be able to identify and advertise
user interface modalities.</p>
<p class="requirement" id="req8">9. Components must be able to solicit and advertise
user choice.</p>
<p class="requirement" id="req10">10. Origin servers must be able to identify and
advertise different representations they may have available.</p>
</div>
<div class="div4">
<h5><a id="d0e248" name="d0e248" />2.2.2.2 Non Web Applications</h5>
<p>In the mobile Internet, just like the Internet as a whole, communication between a
client and a server is not confined to Web applications. In the mobile world,
however, use of HTTP as a bearer for other applications is, if anything, even more
prevalent. Services are often designed this way as a result of there being no access
to TCP sockets on clients, or fears of non-transparency of gateways. Examples
include:</p>
<ul>
<li>
<p>J2ME client applications</p>
</li>
<li>
<p>native applications (Symbian for Symbian devices, Microsoft for Microsoft
devices, etc.)</p>
</li>
<li>
<p>Adobe Flash applications</p>
</li>
<li>
<p>SVGT documents</p>
</li>
<li>
<p>Ajax applications embedded in HTML</p>
</li>
</ul>
<p>There are many other examples, but these are sufficient to illustrate a point: not
all clients using HTTP as a communication protocol with an origin server are
interested in "content transformation". In fact, transformation may break the
semantics of the client-server communication and render the application completely
useless.</p>
<p class="requirement">See <a href="#req6">Requirement 6</a> above.</p>
</div>
<div class="div4">
<h5><a id="d0e276" name="d0e276" />2.2.2.3 Legal, Moral and Commercial Issues</h5>
<p>A further issue concerns the limits of acceptable content transformation and to
what degree content providers can reasonably expect to remain in control of how
their content is presented.</p>
<p>Some content providers may feel that, for whatever reason, their content should not
be fragmented, or their images removed or transformed. In a medical application, for
example, it may be essential that an image is presented in its original format.</p>
<p class="requirement">See <a href="#req6">Requirement 6</a> above.</p>
<p>An example of the commercial issues is removing advertising banners from the origin
server and perhaps even replacing them with new advertisements adapted for the
specific user agent. This is obviously controversial because it hi-jacks an
advertising revenue stream from the origin server.</p>
<p class="requirement" id="req11">11. It must be possible for origin servers
selectively to indicate that content of various types must not be removed, replaced
or inserted by transforming proxies.</p>
</div>
<div class="div4">
<h5><a id="d0e292" name="d0e292" />2.2.2.4 Security Issues</h5>
<p>The most commonly used security mechanisms require a direct connection between the
origin server and the ultimate client. Intermediaries of any kind, including content
transformation proxies, may break this security model and cause exposure to theft of
sensitive information.</p>
<p class="requirement" id="req12">12. It must be possible to establish a secure end to
end connection.</p>
</div>
</div>
</div>
</div>
<div class="div1">
<h2><a id="constraints" name="constraints" />3 Constraints</h2>
<p>The BPWG, and hence the Content Transformation Task Force, is not chartered to create
"new technology", rather it is chartered to advise on the use of existing technology.
Hence the techniques should operate within existing technology. That said, the Task Force
is free to suggest new mechanisms and enhancements to existing mechanisms to other W3C
groups that are chartered with the development of such technology.</p>
<p>Examples of technologies and techniques that will be further investigated include, but
are not limited to:</p>
<ul>
<li>
<p>The HTTP protocol <a href="#HTTP">[HTTP]</a>, which provides several mechanisms that
are likely to be useful. In particular to promote awareness of the "<a
href="http://tools.ietf.org/html/rfc2616#section-14.9.5">Cache-Control:
no-transform</a>" HTTP directive, or other mechanism for allowing content authors to
prohibit transformation of a resource by intermediaries.</p>
</li>
<li>
<p>The <a href="http://www.w3.org/2007/powder/">POWDER</a> protocol, which provide
mechanisms for describing resources using RDF and OWL. More generally, ascertaining
that a representation of a resource is suitable for the user's delivery context either
because the resource has been so described or from the nature of the representation of
the resource.</p>
</li>
<li>
<p>mobileOK (see <a href="#mobileOKBasic10Tests">[mobileOKBasic10Tests]</a>) which is a
claim that can be represented using (POWDER) Web Description Resources, that a
resource achieves certain minimum interoperability requirements for mobile
delivery.</p>
</li>
<li>
<p>The work of the <a href="http://www.w3.org/2005/MWI/DDWG/">W3C MWI DDWG</a> relating
to definition of device capabilities.</p>
</li>
</ul>
</div>
</div>
<div class="back">
<div class="div1">
<h2><a id="terminologyNote" name="terminologyNote" />A Terminology (Non-Normative)</h2>
<p>In <a href="#HTTP">[HTTP]</a>, <a href="http://tools.ietf.org/html/rfc2616#section-1.3"
>1.3 Terminology</a> various types of intermediary are described:</p>
<dl>
<dt class="label">Proxy</dt>
<dd>
<p>A proxy is a forwarding agent, receiving requests for a URI in its absolute form,
rewriting all or part of the message, and forwarding the reformatted request toward
the server identified by the URI.</p>
</dd>
<dt class="label">Gateway</dt>
<dd>
<p>A gateway is a receiving agent, acting as a layer above some other server(s) and, if
necessary, translating the requests to the underlying server's protocol.</p>
</dd>
<dt class="label">Tunnel</dt>
<dd>
<p>A tunnel acts as a relay point between two connections without changing the messages;
tunnels are used when the communication needs to pass through an intermediary (such as
a firewall) even when the intermediary cannot understand the contents of the
messages.</p>
</dd>
</dl>
<p>The term "content transformation proxy" has become popular for a special type of gateway:
one that transforms content as described above. The term "content transformation gateway"
would perhaps have been a better choice or maybe even "content transformation proxy
gateway", since the relevant server technology actually is both a proxy and a gateway.</p>
</div>
<div class="div1">
<h2><a id="d0e364" name="d0e364" />B References (Non-Normative)</h2>
<dl>
<dt class="label"><a id="BestPractices" name="BestPractices" />BestPractices</dt>
<dd>Mobile Web Best Practices 1.0 Basic Guidelines, Jo Rabin, Charles McCathieNevile (eds), W3C Recommendation, 29 July 2008 (See <a href="http://www.w3.org/TR/2008/REC-mobile-bp-20080729/">http://www.w3.org/TR/2008/REC-mobile-bp-20080729/</a>)</dd>
<dt class="label"><a id="mobileOKBasic10Tests" name="mobileOKBasic10Tests"
/>mobileOKBasic10Tests</dt>
<dd>W3C mobileOK Basic Tests 1.0, Sean Owen, Jo Rabin (eds), W3C Recommendation, 08 December 2008 (See <a href="http://www.w3.org/TR/2008/REC-mobileOK-basic10-tests-20081208/">http://www.w3.org/TR/2008/REC-mobileOK-basic10-tests-20081208/</a>)</dd>
<dt class="label"><a id="HTTP" name="HTTP" />HTTP</dt>
<dd> Hypertext Transfer Protocol -- HTTP/1.1 Request for Comments: 2616, R. Fielding, J.
Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, T. Berners-Lee, June 1999 (See
http://tools.ietf.org/html/rfc2616.)</dd>
</dl>
</div>
<div class="div1">
<h2><a id="d0e374" name="d0e374" />C Acknowledgments (Non-Normative)</h2>
<p>The editors acknowledge contributions of various kinds from members of the MWI BPWG <a
href="http://www.w3.org/2005/MWI/BPWG/Group/TaskForces/CT/">Content Transformation Task
Force</a>.</p>
<p>The editors acknowledge significant written contributions from:</p>
<ul>
<li>Magnus Lonnroth, Drutt</li>
</ul>
</div>
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