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This document is the Problem Statement referred to in the Charter of the W3C Mobile Web Inititiative Best Practices Working Group Content Transformation Task Force. It acts as the specification of the requirements for the guidelines referred to in that Charter.
This document is an editors' copy that has no official standing.
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 http://www.w3.org/TR/.
This draft is a work in progress and has not been approved by the BPWG. It is the first internal draft.
This document has been produced by the Content Transformation Task Force of the Mobile Web Best Practices Working Group as part of the Mobile Web Initiative . Please send comments on this document to the Working Group's public email list public-bpwg-ct@w3.org, a publicly archived mailing list .
This document was produced under the 5 February 2004 W3C Patent Policy . The Working Group maintains a public list of patent disclosures made in connection with 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 must disclose the information in accordance with section 6 of the W3C Patent Policy.
1 Introduction
2 The problem
3 Constraints
A References (Non-Normative)
B Acknowledgements (Non-Normative)
Many web sites provide pages that do not work well on mobile devices. These pages are intended to be viewed only by desktop browsers. Typical of the problems encountered when trying to access such pages with a mobile device are: that the page layouts assume a screen larger than the device supports; that the pages require more memory than the device supports; that a full querty keyboard and mouse are required to use the page; or, that the page uses content types that the device does not support. These sites will either send such a pages to the mobile device, which will try to display it, or send an HTTP error status code. These sites can be referred to as mobile unaware sites.
Content transformation proxies, situated in the communications path between the mobile device and the web site, are able to transform the content of such pages to enable effective display and use on mobile devices. Many parties, including mobile operators and search engines, are introducing content transformation proxies to allow mobile device users to access the bulk of sites and pages on the Internet.
Content transformation proxies typically work by masquerading as desktop browsers, fetching content and then modifying it before returning it to mobile devices. These transformations range, for example, from simple character set corrects, through image reformatting and resizing, layout modifications and page segmentation, to multi step JavaScript transaction emulation. Content transformation proxies can also add content to, or remove it from a page.
While this approach is very effective for mobile unaware sites, it presents on obstacle to mobile aware sites which provide content intended for mobile devices. The masquerading technique prevents mobile aware sites from detecting the mobile devices that originate requests; the sites only detect a desktop browser. Mobile aware sites may provide mobile compatible pages or mobile compatible content like ring-tones or Java applications. The designers of such sites may prefer any content transformation proxies leave both the mobile devices request and the returned content unchanged. Some sites may cater for both desktop browsers and mobile devices. In these cases the user of a mobile device may prefer to choose which site he or she accesses.
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.
Techniques are needed to enable content transformation proxies to be used, so that mobile devices can access both mobile aware sites and mobile unaware sites, providing mobile device users the maximum possible access to the Internet.
Techniques need to be identified or designed to enable the following:
Identify what representations are available for a resource.
Indicate a user's or site designer's intent to intermediary proxies.
Identify mobile content in a response.
JR: I am wondering whether we should avoid reference specifically to "mobile" throughout this document, and generalise to "the users delivery context". Clearly there needs to be an explanatory note saying that our focus is mobile, but there is no hard and fast dividing line between what is mobile and what is not.
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 (using a WDR or some other type of label), or from the nature of the representation of the resource.
Enable site designers to provide content transformation hints to intermediary proxies, e.g. to identify the "most important" parts of a resource.
In particular to promote awareness of the "Cache-Control: no-transform" HTTP directive, or other mechanism for allowing content authors to prohibit transformation of a resource by intermediaries.
Elaborate an origin server's description of a resource (WDR, label etc.) to allow intermediaries to adjust the description of the properties of the resource when accessed via those intermediaries.
Identify all actors in the delivery context so that they can find out about each other
Identify the originating user agent and its capabilities to intermediary proxies and the origin server
Identify an intermediary proxy's capabilities (including transformation capabilities) to other intermediary proxies and the origin server
While providing accurate User Agent information, work effectively with an origin server that is unaware of the negotiation techniques described above, and so avoid that server responding that it does not support a User Agent.
When considering these issues to take into account the work of the W3C MWI DDWG relating to definition of device capabilities.
If necessary note the need for a consistent representation of device and intermediary capabilities.
Enable user control of the experience - e.g. deciding whether they want the desktop or mobile experience when there is a choice, noting that while it is important to make assumptions about the user's context to try to provide an appropriate experience, those assumptions may be wrong.
The impact of content transformation on security needs to be considered and any recommendations made. In particular, consideration needs to be given to the possibility of "man in the middle" security attacks.
The implications of operations such as advert insertion and similar changes to original content needs to be considered and any recommendations made.
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.