Mobile Web Best Practices Working Group News

Content Transformation guidelines - working draft — 15 April 2008

The Mobile Web Best Practices Working Group has published the first public working draft of the Content Transformation Guidelines document.

As stated in the abstract of the document:

The document provides means for content providers and content transformation proxies as to how inter-work when delivering Web Content.

In other words, the guidelines are mechanisms:

  1. for content providers to be able to provide media-specific versions of their site based on the end-user's device, no matter if the request and response go through one or more content transformation proxies
  2. for content transformation proxies to let former point happen while still be given the possibility to adapt legacy web sites that would reject the user's request as it stands because it originates from an "unusual" device.

Guidelines in the published document do not differ from the ones I mentioned in my previous post on content transformation. Among them:

  • Content Transformation proxies must leave the HTTP request (resp. response) untouched if the HTTP request (resp. response) contains a Cache-Control: no-transform directive (see §4.1.1 and §4.4). To be more precise, it must behave as a transparent proxy in that case.
  • Content Transformation proxies should not alter the HTTP headers unless the unaltered user's request would end up being rejected by the content provider (see §4.1.2)
  • If if has altered HTTP headers, the proxy must include copies of the unaltered ones (see §4.1.4)

The document is intended to be clear and concise (although some more work may be needed on that regard in a few sections). Editorial notes in the document mark parts that are not settled yet.

The working group is looking forward for comments on these guidelines. If you think something is wrong, missing, unclear, feel free to send an email to

Francois Daoust 1 comment Permalink

Comments, Pingbacks:

Comment from: Umesh Sirsiwal [Visitor]
Several content transformation proxies and the Internet in general includes forward caches. Current definition of HTTP includes indication of transformation using Vary header. In most cases the Content Transformation proxies and servers vary their responses based on User-Agent header. The number of User-Agent string in is very high and caches cannot possibly store these mean copies of the response. Most servers are likely to classify the devices in certain meta-groups for the purpose of content transformation. However, this meta-group is expected to be server specific. In absence of formal method, the caches will be left to guess the meta-group. What will be the method to solve this?
PermalinkPermalink 2008-05-19 @ 14:48

Contacts: Daniel Appelquist, Jo Rabin, Chairs
Dominique Hazaël-Massieux and François Daoust, W3C Team Contacts