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Re: XPointer considered incomprehensible

From: Bjoern Hoehrmann <derhoermi@gmx.net>
Date: Tue, 05 Sep 2006 01:08:50 +0200
To: ht@inf.ed.ac.uk (Henry S. Thompson)
Cc: www-xml-linking-comments@w3.org
Message-ID: <9obpf2tsp0pf5sech8eh46o9en0j8j15o0@hive.bjoern.hoehrmann.de>

* Henry S. Thompson wrote:
>That's not how I read it -- for any URI scheme, documentation of a
>fragment identifier syntax has to explain _how_ it identifies a
>secondary resource.  That's what the XPointer specs. do.  The issue of
>discontinuous/multiple secondary resources is a separate matter, on
>which I still owe you a reply.

I'm just saying that simply replacing "subresource" with "secondary
resource" does not make the specification much clearer for me. That
there are multiple ways to read the specification is exactly my
problem. 

>Success/failure of syntactically OK pointer parts to identify is
>always an empirical question (just as for element(intro) above).  The
>only way to find out if a pointer part identifies a secondary resource
>is to pass it to a implementation of the scheme and look at the
>result.

You are answering the question from a user point of view, I was asking
from the specification reader and implementer point of view.

>That question is surely up to the spec. of a scheme to make clear.
>Reasonable persons might differ on this one -- seems to me if I were
>speccing this one I'd treat an empty node set as failure to identify
>a secondary resource.

This basically amounts to saying that the definition of each scheme
must define whether a given pointer part identifies a "subresource"
or not, since otherwise you have no way of knowing whether your
XPointer processor needs to look at the next scheme (if any). This
requirement is not, however, part of the specification, and some of
the schemes don't address this. The xpointer() scheme itself does
not seem to define this, for example.

>I'll take this suggestion to the Architecture Domain in the Team (note
>that the Registry is not the responsibility of the XML Core WG), but I
>have to say it's not a direction I personally would like to see us go
>- -- at the time XPointer went to REC we were asked, by several Members,
>to provide a way to broker contention for scheme names for public use.
>The current Registry provides just that.  I understand that you would
>like to see it provide more than that, but that involves taking on
>responsibility, one way or another, for the quality of the schemes
>themselves, and I don't think that makes sense from a cost/benefit
>perspective.

The xpath2 scheme does not have a definition that allows me to im-
plement it. If I want to offer XPath2-based XPointer capabilities
in my implementation I'd have to either convince the owner of the
scheme to fix the specification, or make a new scheme (like xpath20)
with a adequate specification. As such, for the community, the scheme
provides virtually no benefit and a very high cost. There are of
course other stakeholders here, but other naming schemes and/or
registration requirements would address their needs adequately. In
any case, having schemes like 'xpath2' with no adequate definition
is too high a cost for the community.
-- 
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
Weinh. Str. 22 · Telefon: +49(0)621/4309674 · http://www.bjoernsworld.de
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Received on Monday, 4 September 2006 23:09:07 GMT

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