Re: [apps-discuss] Retroactive application of draft-ietf-appsawg-uri-scheme-reg - comprehensive review

["Roy T. Fielding" <[e-mail]>]

> On Apr 10, 2015, at 8:38 AM, Barry Leiba <[e-mail]> wrote:
> 
>> No scheme can prohibit fragments. They are not part of the scheme's syntax.
> 
> We continue to have a confusion between syntax and semantics here.
> 
> I absolutely agree that no scheme can say that fragments are
> syntactically invalid, because the schemes do not control the syntax
> of a URI.
> 
> But a scheme can certainly say that fragments make no semantic sense
> within that scheme, and that if a URIs uses that scheme and contains a
> fragment, it is not a well formed URI within that scheme.

No, they can't, or at least they cannot say that truthfully.

> It's rather like saying that English words are composed of characters
> from the set "abcdefghijklmnopqrstuvwxyz", and, therefore, the string
> "qwx" is a valid piece of an English word (syntax)... but that, in
> fact, no valid English words contain "qwx" (semantics).

Sorry, you've lost me.

It is more like saying that, because host and port are adjacent to each other in
the syntax, it is therefore possible for DNS to specify what ports are allowed.

> That's not a layering violation at all -- it has to be up to the
> scheme to say what the semantic meaning of a fragment is within that
> scheme, or whether fragments have any meaning at all.

It has nothing to do with the scheme. Nothing whatsoever. It is true that there
are many resources, regardless of scheme, for which a fragment identifier wouldn't
have much practical purpose other than as a name, but that's only because
nobody has found a reason to resolve them yet. In most cases, this is because
deployment of the scheme is so small that it isn't worth anyone's bother to create
a gateway for information about its identified resources.

The problem is that if we let people write incorrect statements about fragments
within scheme specifications, we lose interoperability around one of the main
extension points in Web architecture. We lose the ability to process the results
of interactions independently of the protocols and systems used to obtain them.

....Roy