Re: JSON-LD onsite examples: are @context values missing a trailing slash?

> On Feb 19, 2015, at 6:39 AM, Dan Brickley <> wrote:
> On 17 February 2015 at 23:30, Gregg Kellogg <> wrote:
>> This isn't a JSON-LD heuristic, but a general web server mechanism to handle
>> ill-formed URLs. As it happens, although it's common practice,
>> is not a valid URL, as it doesn't have a path component.
> Which URL spec are we going by here? Lots of URLs lack path components.
> e.g. 3.3 of says
> "If a URI contains an authority component, then the path component
>   must either be empty or begin with a slash ("/") character."
> Or HTTP URIs per RFC-7230 "Hypertext Transfer Protocol (HTTP/1.1):
> Message Syntax and Routing" which largely defers to that work:
> """
> 2.7.  Uniform Resource Identifiers
>   Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
>   HTTP as the means for identifying resources (Section 2 of [RFC7231]).
>   URI references are used to target requests, indicate redirects, and
>   define relationships.
>   The definitions of "URI-reference", "absolute-URI", "relative-part",
>   "scheme", "authority", "port", "host", "path-abempty", "segment",
>   "query", and "fragment" are adopted from the URI generic syntax.  An
>   "absolute-path" rule is defined for protocol elements that can
>   contain a non-empty path component.  (This rule differs slightly from
>   the path-abempty rule of RFC 3986, which allows for an empty path to
>   be used in references, and path-absolute rule, which does not allow
>   paths that begin with "//".)  A "partial-URI" rule is defined for
>   protocol elements that can contain a relative URI but not a fragment
>   component.
>     URI-reference = <URI-reference, see [RFC3986], Section 4.1>
>     absolute-URI  = <absolute-URI, see [RFC3986], Section 4.3>
>     relative-part = <relative-part, see [RFC3986], Section 4.2>
>     scheme        = <scheme, see [RFC3986], Section 3.1>
>     authority     = <authority, see [RFC3986], Section 3.2>
>     uri-host      = <host, see [RFC3986], Section 3.2.2>
>     port          = <port, see [RFC3986], Section 3.2.3>
>     path-abempty  = <path-abempty, see [RFC3986], Section 3.3>
>     segment       = <segment, see [RFC3986], Section 3.3>
>     query         = <query, see [RFC3986], Section 3.4>
>     fragment      = <fragment, see [RFC3986], Section 3.5>
>     absolute-path = 1*( "/" segment )
>     partial-URI   = relative-part [ "?" query ]
>   Each protocol element in HTTP that allows a URI reference will
>   indicate in its ABNF production whether the element allows any form
>   of reference (URI-reference), only a URI in absolute form
>   (absolute-URI), only the path and optional query components, or some
>   combination of the above.  Unless otherwise indicated, URI references
>   are parsed relative to the effective request URI (Section 5.5).
> """
> As far as I can see the absolute-path construction is only used in
> non-URL settings i.e. protocol headers.
> My reading is that in JSON-LD '' serves to identify
> an URL from which a context can be acquired. We have wired up the
> relevant server-side voodoo such that this works e.g. via: curl -H
> "Accept: application/ld+json"
> ... where is it written that is a bad http URL?
> (genuine question not rhetorical :)

Yes, I stand corrected, path-abempty is defined as *( "/" segment) so the empty string is indeed legitimate; however, it is not in normal form.  From 6.2.3 [1]:

 In general, a URI that uses the generic syntax for authority with an empty path should be normalized to a path of "/".

As Kingsley points out, though <> and <> are two different resources in the strict RDF sense. From a linked data perspective, how this is interpreted depends on  the response is a 200, 301, 303 or 304 in terms of how how relative URLs in the retrieved resource are interpreted. With all intention of averting a perma-thread, RFC3986 does indicate that a redirect from, say, <> to <> indicates that they are equivalent resources. Not redirecting doesn't really say anything. It also says that when comparing URLs they should be normalized, and in 6.2.3 [1] specifically says that <> and <> are equivalent (because of the definition of the HTTP scheme).

RFC2616 3.2.2 goes on to say [2]:

If the abs_path is not present in the URL, it MUST be given as "/" when used as a Request-URI for a resource (
section 5.1.2)

But, this is how a server should treat such a request.

It also says:

An empty abs_path is equivalent to an abs_path of "/".

This comes down to what should be promoted as best practice, but IMO, the <> meme is out there in the public, and isn't likely to go away any time soon. In our examples and literature, however, it might be best to stick with using <>.

In any case, for the use in @context, is legitimate (though not normal) and will be interpreted by implementations the same as For use in @vocab, or in a prefix definition, the trailing slash _is_ important.


> An equal counter question: where is it written that such an url would
> be dereferenced by requesting '/' ? Or is this just a convention?
> Dan
> ps. anyone studied HTTP2's for these issues yet?

Received on Thursday, 19 February 2015 20:26:22 UTC