W3C home > Mailing lists > Public > public-bpwg-ct@w3.org > September 2008

LC-2007: use of MUST when referring to the role of the server

From: Francois Daoust <fd@w3.org>
Date: Mon, 15 Sep 2008 10:53:16 +0200
Message-ID: <48CE227C.5000601@w3.org>
To: public-bpwg-ct <public-bpwg-ct@w3.org>

The Last Call comment:

As text:
"The use of MUST on the CTG when referring to the role of the server
should not be allow, since irresponsible transcoding companies will use 
this to disrupt service and destroy the user experience set us back many 
We can accept RECOMMENDED, and only RECOMMENDED."

For the time being, there are two uses of MUST in section 4.2 Server 
Response to Proxy:
1/ "Servers MUST include a Cache-Control: no-transform directive if one 
is received in the HTTP request."
2/ "If a server varies its representation according to examination of 
received HTTP headers then it MUST include a Vary HTTP header indicating 
this to be the case"

Both uses depend on the resolution of other comments, and in particular:
- LC-2080, LC-2041 for 1/
- LC-2079 on profiling HTTP for 2/ (even though it deals with returning 
406 responses, I'd say it also applies to the Vary HTTP header which is 
not required by the HTTP RFC)

Depending on how we resolve the above comments, the comment may thus 
turn out to not to apply to the spec anymore. Let's suppose it still 

I do not see any reason not to use MUST for servers as well, when 
required. What we are basically saying here is that a CT-proxy cannot 
tell for sure what a server has in mind in 100% of all cases. A server 
may not conform to the guidelines, that's its choice. The remaining 
guidelines (that apply to the CT-proxy) are here to make things work as 
much as possible when servers are not aware of the existence of the 
guidelines. There is a way for servers to get closer to 100% by 
following these guidelines. It involves some dos and don'ts. Claiming 
conformance to the guidelines and not following "SHOULD" statements 
requires a justification as well. The comment seems to imply that, 
provided we only use "SHOULD and MAY" statements, ALL servers would be 
conforming to the guidelines by default, and that's not the case. Should 
it be? Maybe, but in that case, the notion of a "Content Deployment" 
class of product doesn't mean a lot and should be removed altogether, 
and normative statements that apply to servers rewritten as 
non-normative statements.

I think we should start by dealing with the comments on "profiling HTTP" 
because our position on these ones will have consequences for the way we 
can resolved this comment, IMO.

Received on Monday, 15 September 2008 08:53:51 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 20:06:30 UTC