Re: 404 Re: Comments on the Triple Patterns Fragments draft

Looking at the Section 4.2.2 HTTP GET and HEAD in Triple Patterns Fragments
draft,

[[reply with status code 404 Not Found if the fragment (page) with the
given URL does not exist or is empty, i.e., no triples match the selector.]]

If I understand correctly, these two scenarios are bit different and it
might be useful differentiate those two, isn't it? The former could be
because I used a wrong template or mistyped something but in the latter
case the fragment is actually valid but it just happen to be empty. So may
be for the latter "204 No Content" would be a better response so that the
client knows the reason.

[[reply with status code 404 Not Found if the selector is invalid i.e., the
parameter values are not in the domain of the selector. This is the case
if, for instance, a literal is used as subject. ]]

In this case, isn't it better to send a '400 Bad Request' rather than a
'404 Not Found'. I can see why 404 could be technically correct because
that fragment URL doesn't exist but may be it is more helpful to the client
to know the reason.

Looking at the definitions in RFC7231, it seems 404 could be used for all
the aforementioned scenarios but may be it is useful to differentiate those
using the response codes.
[[
The 400 (Bad Request) status code indicates that the server cannot or will
not process the request due to something that is perceived to be a client
error (e.g., malformed request syntax, invalid request message framing, or
deceptive request routing).
The 404 (Not Found) status code indicates that the origin server did not
find a current representation for the target resource or is not willing to
disclose that one exists.
The 204 (No Content) status code indicates that the server has successfully
fulfilled the request and that there is no additional content to send in
the response payload body.
]]

Best Regards,
Nandana

On Wed, Jul 30, 2014 at 11:34 AM, Andreas Kuckartz <a.kuckartz@ping.de>
wrote:

> Ruben Verborgh:
> >> "The 4xx (Client Error) class of status code indicates that the client
> >> seems to have erred."
> >> http://tools.ietf.org/html/rfc7231#section-6.5
> >>
> >> An empty page or fragment is (normally) not a result of an error. Any
> >> 4xx code therefore is (normally) inappropriate.
> >
> > Depends on how you look at it.
> >
> > Client: "Give me the fragment with selector ?x rdf:type ex:Alien."
> > Server: "You asked for something that didn't exist. That's an error."
> >
> > In other words, 4xx errors are those that only a client can fix.
> > And indeed, the client can fix by asking a different fragment.
>
> Well, I think that it is perfectly legitimate and not erroneous to ask a
> server to provide a set of all aliens.
>
> And in this concrete case the server very likely _can_ provide a
> non-empty set by using improved SETI techniques !
>
> Cheers,
> Andreas
>
>