Re: [xml-dev] xml:base and fragments

[Michael Kay <mike@saxonica.com>]

> On 9 May 2017, at 16:46, Andrew S. Townley <ast@atownley.org> wrote:
> 
> 
> The specific portions of RFC 3986 that are most relevant to this discussion are Sections 4.4, Same-Document Reference, and Section 5.1 Establishing a Base URI.
> 
> The rest of Section 5 defines operations and examples on how to actually create a complete URI based on having a base URI and some URI fragment, so they’re independent of exactly HOW the base URI was identified in the first place.
> 
> The crux of this whole question/discussion seems to be Section 5.1 that describes 4 ways to establish a base URI. 

I don't think there's much dispute about how to establish a base URI and how to use it to resolve a relative reference. The crux to me is section 4.4 on same-document reference, which talks about using (dereferencing) the (resolved, absolute) URI to obtain a resource, and here it gives the surprising rule that if:

* the base URI is http://A/

and

* the URI you are dereferencing is http://A/

then

* the reference is interpreted as a reference to the entity containing the reference, even if that entity is completely unrelated to anything you might find by retrieving the resource at http://A/. 

But this rule only applies if "the URI reference is dereferenced for a retrieval action". I think this phrase has to be read in the light of 1.2.2, which says:

Given a URI, a system may attempt to perform a variety of operations
   on the resource, as might be characterized by words such as "access",
   "update", "replace", or "find attributes".  Such operations are
   defined by the protocols that make use of URIs, not by this
   specification.

and this means that if a higher-level protocol chooses to define an operation (say "access" or "fetch") as behaving differently from a "retrieval action" in the sense defined by the RFC, then it is at liberty to do so.

Michael Kay
Saxonica