Re: Issue 39: proposed example for varying the etag based on conneg

On 06.04.2010 17:22, Jamie Lokier wrote:
> ...
> Changing attribute order *is* making a different representation.
>
> Thus Julian's idea of when to use the same weak etags is recommended
> against by Yves.
> ...

Nope.

It is a different representation (in that it may vary over time), but I 
wouldn't call it a different representation of a different *resource*.

> I happen to agree with Julian(*), but I'm really interested in when
> Yves thinks it is appropriate to use same weak etags, given the
> statement that it's unsafe to use them for different representations.
>
> -- Jamie
>
> ps. (*) Why my pov matches Julian's:
>
> Instead of changing attribute order, what about different output
> encodings at serialization time?  Note that the *input* XML database
> might not even *have* a character encoding.  I think that is in the
> same category as attribute order, because the underlying XML resource,
> right down to the individual characters, is unchanged, although it's
> clearly not binary identical.

Absolutely.

> If the underlying resource is the same for different character
> encodings (Content-Type charset=), in what way is compression
> (Content-Encoding) semantically different?  I think it isn't.

I'm not sure, and I'm even not sure the answer matters.

We will need to change text to address 
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/101> (please review 
the long history of this issue).

In particular, Roy said:

> A weak entity tag SHOULD change whenever the origin server considers prior representations to be unacceptable as a substitute for the current representation. In other words, an entity tag SHOULD change whenever the origin server wants caches to invalidate old responses.

Best regards, Julian