root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = SUCCEEDED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py
             product   file:work.py
             product   step:cp -p data/inp.txt out.txt

file:work.py
               state = CONFIRMED
             creator   step:./plan.py
                sink   (step:./work.py)

(step:./work.py)
               state = PENDING
                need = DEFAULT
           using_env = STEPUP_PATH_FILTER [dynamic]
              source   file:work.py
             product   (st:data/)

step:cp -p data/inp.txt out.txt
               state = SUCCEEDED
                need = DEFAULT
             creator   step:./plan.py
              source   (file:data/inp.txt)
             product   file:out.txt
                sink   file:out.txt

(file:data/inp.txt)
               state = CONFIRMED
             creator   (st:data/)
                sink   step:cp -p data/inp.txt out.txt

file:out.txt
               state = BUILT
             creator   step:cp -p data/inp.txt out.txt
              source   step:cp -p data/inp.txt out.txt

(st:data/)
             creator   (step:./work.py)
             product   (file:data/inp.txt)
