Nick Leverton escribió:
 > I have an application which attempts to describe a tree of TCP subnets,
 > which in essence are not fully accessible from each other.  I have a
 > description of the network in XML as shown in the excerpt below.
 > ...
 >
 > <?xml version="1.0"?>
 > <nodes>
 >   <node id="V9990" ip="1.1.1.1">
 >     <unit id="23" ip="10.10.10.10"/>
 >     <unit id="24" ip="10.10.10.11"/>
 >     <node id="V9991" ip="10.10.10.12">
 >       <unit id="26" ip="192.168.0.1"/>
 >       <unit id="27" ip="192.168.0.2"/>
 >     </node>
 >   </node>
 >   <node id="V9992" ip="2.2.2.2">
 >     <node id="V9993" ip="10.10.10.10">
 >       <unit id="21"/>
 >       <unit id="22"/>
 >     </node>
 >   </node>
 > </nodes>
 >
 > To simplify network maintenance I would like to use the same config file
 > on all the "nodes", and to modify the XPath query with extra terms on
 > the sub-nodes.  In other words, on the "root" machine a query for id=26
 > will return ip=1.1.1.1, but on node V9990 a query for id=26 will return
 > ip=10.10.10.12
 >
 > In summary, what I want to do is to retrieve the nearest ip attribute
 > in the document which has a given id attribute as a descendant.  I am
 > currently using the following XPath:
 >
Nick Leverton escribió:
> In article <4939431f$0$17068$6e1ede2f@r...>,
> Dimitre Novatchev <dnovatchev@c...> wrote:
>> What do you mean by "nearest"? Is this the geographical distance b/n two 
>> nodes? I dont see this reflected in the XML document.
> 
> No, sorry for being unclear.  I mean that from the set of ip attributes
> on the axis which contains both the root and the required id attribute:
> 
>   / ... @ip ... @ip ... @ip ... @id
> 
> I want to find the left-most one in the above diagram, nearest to the root
> (or to other selected starting node inbetween the root and the required @id).

So you mean: inside the context node, find the IP of the outermost 
"node" that contains the destination "unit". The XPath for this could be 
(untested):

     ./descendant::node[.//unit[@id="26"]]/@ip

Is that what you want?

-- 
Manuel Collado - http://lml.ls.fi.upm.es/~mcollado