Nested Workflows....

I am looking for either a usable design pattern, or
actual functionality that will solve the following any
ideas would be helpful:

Order Workflow:
There are several step involved completing an order
workflow..

From within the context of an order workflow there are
1 to N (unknown) elements of an order that must
complete its own workflow.
once all elements are completed the top level (order
workflow) can continue.
I do not know of any nested workflow tags from the
DTD, nor any Loop logic.

Currently i am implementing a class that i use as a
condition to check if all elements associated to an
order have completed their workflow, before allowing
the wf to move to the next step.  

It seems that this would be a common pattern in a
workflow and wondered if others had come up with a
more elegant solution.  Or if 'nested' workflows or
loops should be built into the workflow descriptor.

Thoughts?

Thanks,
TJ

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