Re: [xsl] Generating a tree

Subject: Re: [xsl] Generating a tree
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Tue, 04 May 2004 17:05:02 -0400
Hi Marcus,

This kind of problem can be a fun challenge.

If you don't have a lot of XSLT experience (and sometimes even if you do), the hard part of a problem like this is knowing which are the hard bits, and which not.

In this case, it's the node selection logic that is the hard part: how do you traverse the tree including just the nodes you want? The easy part is rendering those nodes as you select them. (Indenting can readily be achieved by iterating over ancestors of a node and putting out whitespace for each ancestor.)

So how to select the nodes? One clue can be gotten by keeping in mind that by default the XSLT processor goes top-down, and in fact since this is how you want your rendition to appear, this is the right way to go.

This means translating your logic specifying which nodes you want to include to a top-down model. As it happens, this is pretty straightforward:

starting at the document element (not the root node)
A. process all its children
   with each child encountered:
     if it is an ancestor-or-self of your target node
       mark with 'minus', and
       if it's an ancestor, return to A
       if it's the target node, just write the children
     if not
       if it has children, mark with 'plus'
       in any case, write it out

This reduces the logic to a recursive process that is easily enough achieved using XSLT's processing model. The only trick is in that test: when processing a node, how do you know it's an ancestor of your target node (or the target node itself)?

Assume you have bound your target node to a variable:

<xsl:variable name="target" select="//*[@id='somethingorother']"/>

In this case, a current node "." is among the ancestor elements of the target, or the target itself, if it passes the following test:

count($target/ancestor-or-self::*) = count(. | $target/ancestor-or-self::*)

(If you want to improve efficiency a mite you can bind the left side to a variable, since it's always the same.)

Likewise, the current node "." is the target when

count(. | $target) = 1

(XSLT 1.0 idiom for testing node identity.)

I hope that's enough to get you moving.

Hint: don't traverse up from the target node. Instead, traverse down from the document element, testing as you go. The tests will determine whether to descend any particular branch of the tree.

Another hint: modes are your friends.

Ask again if I'm being too sketchy here. And good luck,

At 04:16 PM 5/4/2004, you wrote:
Hi gurus

I want to generate an "unfolded" tree down to a selected element. So I want to render all ancestors to the selected element and all their siblings but not the siblings children. Also, the root shouldn't be included and I don't want the siblings to the top-level (below the root element) ancestor to be included. Another wish is that if the selected element is a section element I also want to render it's children (just one level though).

Example source XML:

  <section name="level1_1">
    <section name="level2_1>
      <page name="level3_1"/>
    <section name="level2_2"/>
    <page name="level2_3"/>
    <page name="level2_4"/>
    <section name="level2_5">
      <section name="level3_1">
        <page name="level4_1"/>
      <page name="level3_2"/>
      <section name="level3_3"> <-- Selected element
        <page name="level4_1"/>
        <page name="level4_2"/>
      <page name="level3_4"/>
  <page name="level1_2"/>
  <section name="level1_3">

Wanted result (with indents and everything :) :
node name="level1_1"
  node name="level2_1"
  node name="level2_2"
  node name="level2_3"
  node name="level2_4"
  node name="level2_5"
    node name="level3_1"
    node name="level3_2"
    node name="level3_3"
      node name="level4_1" //shouldn't be rendered if page
      node name="level4_2" //shouldn't be rendered if page
    node name="level3_4"

It would also be nice if one could draw something extra to indicate whether the node has children or not (like a plus or minus...).

How would you do it? I've made a couple of tries with anscestor-or-self::etc but I just tangle myself into hairy loops.

The template/templates that will do this will be called on the selected element level.


ps. I'm using MSXML so node-set() is available.

Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.      
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
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