Joining two relative URIs

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

I'm writing to you on behalf of the xml core working group.

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 make c's xml:base an 
absolute URI using the algorithm in 5.2 in RFC 2396 [8].

Note that the above example 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, while ignoring the constraint in 
section 5.2.1 of the same RFC that "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 is discussing the adoption of 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]). Another 
alternative could be to not 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 working 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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