[xsl] Finding paths in Visio XML exports - recursion question

[Steven Davies <xsl-list@xxxxxxxxxxx>]

Hi everyone,

while I'm not a total XSLT newbie I'm having trouble getting my head
round a couple of things when trying to find paths through Visio
flowcharts which have been exported in Visio's XML format.

Very basically, for anyone who is unaware of Visio's schema I shall try
to describe it below with a very simplified example:

<Pages>
 <Page ID="1">
  <Shapes>
   <Shape ID="1" NameU="CustomShape.112">
    <Shape-specific-data />
   </Shape>
   <Shape ID="2" NameU="CustomShape.8">
    <Shape-specific-data />
   </Shape>
   <Shape ID="3" NameU="CustomShape.32">
    <Shape-specific-data />
   </Shape>
  </Shapes>
  <Connects>
   <Connect FromSheet="1" FromCell="BeginX" ToSheet="1" />
   <Connect FromSheet="1" FromCell="EndX" ToSheet="2" />
   <Connect FromSheet="2" FromCell="BeginX" ToSheet="2" />
   <Connect FromSheet="2" FromCell="EndX" ToSheet="3" />
  </Connects>
 </Page>
</Pages>

Obviously there are many more <Shape>s and <Connect>s in the document!
The <Connect>s map from a <Shape> whose ID is the same as @ToSheet and
@FromCell="BeginX" to a <Shape> whose ID is the same as @ToSheet and
@FromCell="EndX".

Now, I can use an XPath expression to find the first node in the
document easily enough (it has a certain property in its data set to
"1") and the only way I've been able to find all connected shapes from
this one is to use 3 for-each loops: the first over all <Connect>s
beginning at the shape itself, the second nested loop over all other
endpoints of the <Connect> (there will only ever be one) and the third
over all <Shape>s connected to the <Connect>:

 <xsl:variable name="thisShapeID" select="./@ID"/>
 <xsl:for-each select="../../v:Connects/v:Connect[@ToSheet=$thisShapeID
and @FromCell='BeginX']">
   <xsl:variable name="connectFromSheet" select="./@FromSheet"/>
   <xsl:for-each select="../v:Connect[@FromSheet=$connectFromSheet and
@FromCell='EndX']">
     <xsl:variable name="nextShapeID" select="./@ToSheet"/>
     <xsl:for-each select="../../v:Shapes/v:Shape[@ID=$nextShapeID]">

I had to use the xsl:variables because I couldn't get the equation
[@ID=./@ToSheet], for example, to work (it never matched, any ideas with 
this?).

Inside the innermost xsl:for-each I recursively call the template which
works very well for a straight flow in Visio. However, there can be
infinite loops in the flow so I have to first test whether the <Shape>
has already been output before recursing. This works.

Also the flows can branch off in multiple directions and each branch
needs to be output one at a time (i.e. the nodes before the branch only
need to be output once). This also works.

My problem is that I need to output a message (well, an element - 
eventually this will be XSL-FO) every time the end of a path is reached. 
This could be because the flow looped back, that is, the recursion is 
stopped, or it could be because the end of a branch (and therefore 
outermost for-each) was reached. While this is relatively easy to do, I 
end up getting multiple copies of the node output because of the 
multiple levels of recursion.

Does anyone have an idea how to get around this?

If you have any questions about this please let me know - I'm thinking 
about this on a more conceptual level than practical level as I'd like 
to get my head around it rather than just trying things blindly! 
Unfortunately I can't provide the flowchart as it's confidential but I 
can make a mock-up in the Gimp if anyone thinks it would help.

Many thanks if you got this far ;-)
Steve