Definition: “Simulation is the imitation of some real thing, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviors of a selected physical or abstract system. […] A computer simulation (or ‘sim’) is an attempt to model a real-life or hypothetical situation on a computer so that it can be studied to see how the system works. By changing variables, predictions may be made about the behavior of the system. It is a tool to create a virtual environment of the real time system.” (Wikipedia, 2011) 
Simulation in the ADVENTURE context is the phase where an ADVENTURE process is simulated in a software system, either to make a forecast about the results or to optimize the ADVENTURE process. 
Forecast describes the process of deriving statements and assumptions about states/facts/conditions/circumstances/data in the future based on information available at present. 
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