[kepler-dev] Workflow for recursive algorithm?

[Zhijie Guan]

Hi,

Does anybody have the experience of modeling recursive process using 
Kepler workflow? Any comments/suggestions/ideas are appreciated.

Currently I am trying to model an algorithm which is similar to a tree 
traversing process. Many algorithms involving tree data structrue use 
recursion. Although theoretically any recursive function can be 
transformed into an iterative function by using a stack, it is often 
difficult to transform tree traversing algorithm because the tree may have 
unknown length. So I prefer to explore Kepler's ability of describing 
recursions.

Here comes the pseudo code of the recursive algorithm:

FUNCTION recursiveDCM(tree)
 	IF tree is small enough THEN
 		evaluateTree(tree)
 	ELSE
 		subtrees[] = divideTree(tree)
 		FOR EACH subtree IN subtrees[]
 			recursiveDCM(subtree)	// Recursive call
 		finaltree = mergeTree(subtrees[])
 	END IF
 	return(finaltree)
END FUNCTION

The functions evaluateTree, divideTree, and mergeTree have been 
implemented as actors. I would like to build the function recursiveDCM as 
a workflow. I know it's pretty easy to wrap all the code into one actor 
to implement the recursion since Java itself supports recursion. But I 
would like see if Kepler can handle it.

The first method popped up in my mind is to use CompositeActors. I tested 
my idea with a simple String Concatenate workflow. I firstly built up a 
workflow which includes a StringConstant actor, a StringConcatenate actor, 
and a TextDisplay actor. They are linked as the following:

StringConstant-->InputPort1 of StringConcatenate-->TextDisplay

Then I wrapped the StringConstant and StringConcatenate actors as a 
CompositeActor. So the workflow now looks like:

CompositeActor-->TextDisplay

Then I copied the CompositeActor, open the CompositeActor (look inside), 
and pasted the CompositeActor into the CompositeActor editing interface. 
Then within the CompositeActor editing interface, I connected the output 
of CompositeActor to another input port of the StringConcatenate actor. 
Now the inner structure of the CompositeActor looks like:

StringConstant-->InputPort1 of
                                StringConcatenate -->Outgoing port
                  InputPort2 of
                /
               /
CompositeActor

I hope including a CompositeActor into itself could let me model the 
recursive process. But it does not work as I expected. I checked the 
workflow XML file, this method only adds one more layer of CompositeActor 
into workflow definition.

Does anybody have better solutions to this problem?

Thanks in advance!

Zhijie