W3C home > Mailing lists > Public > public-bpwg-ct@w3.org > October 2007

RE: Scope of CT Guidelines

From: Sean Patterson <SPatterson@Novarra.com>
Date: Tue, 30 Oct 2007 23:34:29 -0500
Message-ID: <687564BB22A3BD46816764F6976BC9FE05F81506@novarrainet2.internalnt.novarra.com>
To: <public-bpwg-ct@w3.org>

My comments are below.

Sean Patterson

> -----Original Message----- 
> From: public-bpwg-ct-request@w3.org [mailto:public-bpwg-ct-request@w3.org] 
> On Behalf Of Jo Rabin 
> Sent: Tuesday, October 23, 2007 12:12 PM 
> To: public-bpwg-ct@w3.org 
> Subject: Scope of CT Guidelines 
> I thought it worth making a note and stimulating further discussion 
> following today's productive CT TF call. 
> I'm worried that if we step into the space of how to do 3 way content 
> negotiation we will be opening the lid on Pandora's box. 

For version 1.0 of the guidelines, I think we should mainly focus on the communication between the CT proxy and the origin server.  However, there are probably also some things we want to say about the communication between the client and the CT proxy.

> The starting point, I think, is that there are three types of component, 
> server, proxy and browser. Each of those can be capable of 
> transformation. Add to this that each of them will independently also be 
> aware or unaware of whatever our guidelines state about how to 
> cooperate. So in theory at least there are 64 different combinations of 
> aware/capable component types in the delivery chain. That's a bit too 
> complicated for my taste. 
> So I wonder if it's worth considering the question of repurposing the 
> presentation separately from markup and formatting fixups? 
> So far as presentation is concerned I think there's a relatively small 
> set of cases, though each of them undoubtedly has its own complexity. 
> Case 1. 
> a) the Server has only a desktop oriented presentation only 
> b) the browser has mobile presentation only 
> A proxy may have a useful role in re-presenting the content. 
> Note though, that in this case, the server's desktop presentation may 
> actually be a universal presentation (call my web pages boring but they 
> are designed to render across all delivery contexts) so in that case the 
> proxy should not interfere either. 

Agreed.  A CT proxy normally should transform desktop content by default in this case.  If the server says something like "Cache-control: no-transform" then the CT proxy should leave the content alone.

An additional note:  In reality there is a spectrum of device and browser capabilities and dividing clients into mobile and desktop capable is somewhat simplistic.  There are many levels of mobile browser capabilities (e.g., WAP-only, subset of HTML with a subset of CSS, etc.).  There are different levels of desktop-capable as well.

> Case 2. 
> a) The Server has both a mobile and a desktop experience 
> b) Client has mobile experience only 
> Server presents mobile experience. Proxy stays out of the way. 

What if the user prefers the desktop content transformed for mobile?  There needs to be a way for the client to specify that it wants the transformed desktop content.

Also, even if the origin server determines that it should present a mobile experience, the mobile experience(s) that an origin server can present may not be suitable for all mobile clients.  There may be a need to do some transformation even on mobile content if that mobile content does not work properly on a given client.

> Case 3. 
> a) The Server has a desktop oriented presentation only 
> b) Client can simulate desktop 
> Client goes ahead and simulates desktop 
> (There is an argument that says that this could land the user in a delay 
> and cost nightmare. So is that an argument against the concept of 
> simulating desktop on a mobile, or is it an argument for saying that 
> there is a role for transforming proxy to reduce that delay and cost 
> nightmare?) 
> Also same case as in 1, where the server has a single presentation, but 
> that presentation is suitable across the board. 

There can be a role for the CT proxy in this case if the user wants transformed content because the original desktop content takes too long to load, is too large for the available memory of the device, etc.  There may also be some desktop content that doesn't work properly on a particular client even if it can handle most desktop content.

> Case 4. 
> a) The server has a choice of presentations 
> b) The client has a choice of presentations 
> The user should be able to get either i) the mobile presentation ii) the 
> simulated desktop presentation. That choice may be triggered by 
> selection locally to the client or at the server. 

As in cases 2 and 3, the user may prefer to get the desktop content transformed for mobile.  If that is the case, the user should be able to get what he/she wants.

> Case 5. 
> Although this looks like a Web request, in fact it isn't. It's some ad 
> hoc protocol xmlhttprequest-like thingy. 
> (Proxy leaves well alone) 

Request and/or response should be marked to tell the CT proxy to avoid any transformations. 

> I'm assuming that this is a more of less complete list of scenarios 
> where the presentation is adjusted at most once. 

Case 6. 
a) Server a choice of presentations 
b) Client can do desktop 

This is similar to case 3.  Server would send desktop content and client may want the CT server to do some transformation of the content so that it loads more quickly, fits into available memory, etc. 

> Now I think that we can consider on top of this whether the proxy has a 
> role adjusting not the presentation, but details of the formatting - 
> e.g. to tweak the content type header, or to tweak the DOCTYPE to avoid 
> problems. Possibly to re-render images from one format to another. 

We should certainly consider these issues. 

> To my mind, that is almost certainly enough to do deal with in volume 1 
> of the guidelines. I think we should leave the door open to later 
> elaborations that discuss 3 way content negotiation, servers 
> deliberately delegating formatting or presentation tasks to proxies and 
> so on. However all that falls firmly in a volume 2. 

I agree with this. 

> I'm hoping that by restricting the initial scope we stand a chance of 
> meeting the proposed timescales for the deliverable, and of addressing 
> in a timely way the key point of the Task Force's existence - which is 
> to provide a way for Transforming Proxies to get out of the way of 
> mobile ready content. 
> Hope this makes sense and looking forward to comments. 
> Jo 
Received on Wednesday, 31 October 2007 04:33:31 UTC

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