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Re: Mandating respect of some heuristics?

From: Francois Daoust <fd@w3.org>
Date: Mon, 01 Dec 2008 10:21:31 +0100
Message-ID: <4933AC9B.3020403@w3.org>
To: casays@yahoo.com
CC: public-bpwg-ct@w3.org

Eduardo Casais wrote:
> The proposal made by Dominique would go a long way towards addressing the grievances of the mobile developers' community, which is seeing finely tailored and mobile-optimized applications being degraded, rendered less usable, or even inoperative because of a number of transcoder deployments. Indeed, "the approach of favoring
> mobile-content creators by default would be a better one for the mobile web ecosystem as a whole."
> 
> Concerning specific issues raised by Dominique:
> 
> 1. Fundamental principle.
> 
> "I think the high-level question behind this practical proposal is whether a mobile CT proxy should be allowed to transform content that was developed with mobile in mind or not."
> 
> The CTG has been developed in the context of adapting desktop content for mobile devices -- hence there is little rationale to allow transformation of mobile content itself. Mobile developers take care to analyze HTTP request headers and rely upon rich device capability databases (WURFL, DetectRight, Volantis, UAProf...) to deliver pages of an appropriate size, in the correct format, with a suitable character encoding, with pictures of the right dimensions, carefully formatted with special style sheets, etc. There is practically nothing CT-proxies can do to improve upon this -- especially since they do not know anything about application semantics, and they basically do not know more about the end-user devices than application servers.
> 

I agree that the question raised by Dom is indeed the key to this.

I add that to consider Content Transformation in a more generic use case 
where "mobile" has different meanings, we would require more semantics 
and communication means that we cannot create for the time being. In the 
mean time, since the main use case of CT right now seems to be the 
long-tail of legacy Web sites which are simply unaware of mobile 
devices, mandating heuristics to protect mobile content where it can be 
truly identified as this seems to be a safe approach.

In short, I agree with Dom and Eduardo.



> 2. Interpretation of heuristics.
[...]
OK


> 3. Allowable operations.
> 
> "A CT proxy shouldn't apply any non-trivial transformation (with an explicit list of these; e.g. only compressing/removing extraneous white space would be allowed)."
> 
> One might consider allowing "tidying" -- in the sense of correcting violations of well-formedness. And one MUST allow the transformations explicitly specified by standards. I mentioned two applying to WML: encoding to WBXML and converting WML 1.x to WML 2.0. 

IMO, if we go down the road of mandating heuristics, we should refrain 
from introducing exceptions to the rule. If the rule is "no 
restructuring and no recoding", then encoding to WBXML falls under 
"optimizing" and would be allowed. Conversion from WML 1.x to WML 2.0 
already goes too far, I think. Since Content Providers who serve WML 
content are mobile-aware, then we should just leave it to them to choose 
when to serve WML  and when to serve XHTML-MP.

The same goes with tidying. Tidying may actually introduce major changes 
in the content, and there is not "one" way to tidy content, so the user 
agent may eventually not display the tidied content as it would have 
displayed the non-tidied one.


> 
> The important point to realize is that once the enclosing markup is protected from transformations, then its embedded objects should be off limits too (images, scripts, style sheets, etc).

Right, we do have a similar statement for requests in "4.1.5.4 Sequence 
of Requests", and should have something similar for responses.


Francois
Received on Monday, 1 December 2008 09:22:09 UTC

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