Hi Norbert, your question is explained in our PET bottle example http://www.openlca.org/wp-content/uploads/2016/10/1.5-Basic-Modelling.pdf
Processes are sets of interacting activities that transform inputs into outputs. Every process is defined by an output flow as a quantitative reference with the flow type “product flow”, which is either selected or created when creating a project. openLCA distinguishes two types of processes:
System processes in the model graph are framed with a double line (left), unit processes are framed with one line (right).
Whether you are dealing with a system process or a unit process is also indicated by the symbol before the process. Purple background, white letter = system process; White background, purple letter = unit process;