Joining two relative URIs (public-ietf-w3c-draft)

Dear all,

as links in the text are looking ugly in the mailing list archive I'll 
rather post the following "text-only" version. I plan to post right 
after Wednesday's conference call.

best regards
Konrad Lanz

#--- snip ---
Dear T. Berners-Lee, R. Fielding, L. Masinter,

According to an email by John Boyer [1] we need to apply the inheritance 
rule[2] to xml:base when canonicalizing a XPath node-set over a XML 
document using C14n's [3] successor Canonical XML 1.1 [4]. This can be 
critical when nodes in a document become an orphan. For a simple example 
cf. to the post by Henry S. Thompson [5] where critical xml:base context 
could be lost by for instance applying an XPath-Filter[6] (XPath-Filter 
2.0 [7]).

Consider the following

<a>
  <b xml:base="test1/somefile1.ext#abc?def">
    <c xml:base="test2/somefile2.ext"/>
  </b>
</a> 

with the 'b' being clipped out, we'd get

<a>
   
     <c xml:base="test1/test2/somefile2.ext"/>
  
</a> 

and the relevant information of xml:base gets pushed down to the child nodes.

If b's xml:base was an absolute URI one would absolutize using the 
algorithm in 5.2 in RFC 2396 [8]. However the example above requires the 
joining of two relative URIs which we believe is not defined in RFC 2396 
[8]. It may nevertheless be defined in RFC 3986 [9] in section "5.2. 
Relative Resolution" by applying applying the algorithm in 5.2 ignoring 
the note "that only the scheme component is required to be present in a 
base URI".

Our question is: Is this covered in the scope of RFC 3986 [9] ?

The group currently discusses the resolution above as an alternative to 
adapting section 5.2 step 6 [10] of RFC 2396 [8]. (currently referenced 
in xml base [11] and C14n [3]) or not to apply inheritance rules [11] at 
all when nodes in a document become an orphan.

Your comments are greatly appreciated.
best regards on behalf of the xml-core-group

Konrad Lanz

[1] http://lists.w3.org/Archives/Public/public-xml-core-wg/2006Mar/0004.html
[2] http://www.w3.org/TR/xmlbase/#resolution
[3] http://www.w3.org/TR/xml-c14n
[4] http://www.w3.org/XML/Group/2006/02/WD-xml-c14n11
[5] http://lists.w3.org/Archives/Public/public-xml-core-wg/2006Mar/0036.html
[6] http://www.w3.org/TR/xmldsig-core/#sec-XPath
[7] http://www.w3.org/TR/xmldsig-filter2/
[8] http://www.ietf.org/rfc/rfc2396.txt
[9] http://www.ietf.org/rfc/rfc3986.txt
[10] 
http://lists.w3.org/Archives/Public/public-xml-core-wg/2006Mar/0041.html
[11] http://www.w3.org/TR/xmlbase/#resolution
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-- 
Konrad Lanz, IAIK/SIC - Graz University of Technology
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Fax: +43 316 873 5520
https://www.iaik.tugraz.at/aboutus/people/lanz
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