ordering elements by IDREFs?

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Subject: ordering elements by IDREFs?
From: "Rodney Waldhoff" <r_waldhoff@xxxxxxxxxxx>
Date: Thu, 27 May 1999 07:59:17 PDT

I have a flat list of tasks, like this:

<tasks>

 <task id="b">
  <label>Task B</label>
  <depends on="a"/>
 </task>

 <task id="a.1" parent="a">
  <label>Task A.1</label>
  <depends on="a.2"/>
 </task>

 <task id="a.2" parent="a">
  <label>Task A.2</label>
 </task>

 <task id="a.2.i" parent="a.2">
  <label>Task A.2.i</label>
 </task>

 <task id="a">
  <label>Task A</label>
 </task>

</tasks>

(Actually, each task is an indepedent file in some directory, the files are concat-ed together to generate the flat list you see here.)

Note that each task may have a single parent, and each may have zero or more tasks that it depends upon, as long as they share the same parent. The tasks appear in an aribrary order (due to the nature of how the document is constructed).

I've built an XSLT stylesheet that converts this flat list into a nested list, according to the parent attribute (by simple recursion over the tasks whose parent attribute equals my id attribute). The result looks like this:

<tasks>
 <task id="b">
  <label>Task B</label>
  <depends on="a"/>
 </task>
 <task id="a">
  <label>Task A</label>
  <task id="a.1" parent="a">
   <label>Task A.1</label>
   <depends on="a.2"/>
  </task>
  <task id="a.2" parent="a">
   <label>Task A.2</label>
   <task id="a.2.i" parent="a.2">
    <label>Task A.2.i</label>
   </task>
  </task>
 </task>
</tasks>

I later convert this nested list into HTML, in a pretty straighforward fashion. The result looks something like this:

1) Task B
2) Task A
  2.1) Task A.1
  2.2) Task A.2
      2.2.1) Task A.2.i

Note that the <depends> element defines a partial order among the children of a given task. (I can, at creation time, restrict the <depends> values so that a task only depends upon its siblings, and that cycles are prevented.) Hence I'd like to be able to display this final list in its logical order, i.e., a task only appears after the siblings it depends upon. E.g., for the above list, this would be:

1) Task A
  1.1) Task A.2
      1.1.1) Task A.2.i
  1.2) Task A.1
2) Task B

I realize there are several total/linear orderings represented by the partial ordering defined by <depends>, but I'm OK with that. E.g., if I've got:

 A -> C            A---C
 B -> C  (which is   /   for the poset friendly)
 B -> D            B---D

Then any of:

A,B,C,D
B,A,C,D
A,B,D,C
B,A,D,C
B,D,A,C

is acceptable.

Can anyone suggest how I might do this? I've played around with logic like 'before I process a task, process all of the siblings upon which the task depends', but this suffers from several problems, at least in my implementations.

I'm using John Clark's XP/XT, and while I'm not entirely opposed to a XT-specific solution, I prefer a parser independent solution if the performance is reasonable.

Thanks,
-rod


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