  Practitioners of simulation, particularly in engineering contexts, in weapons testing, and in climate science, tend to conceptualize the EOCS in terms of verification and validation.  Verification is said to be the process of determining whether the output of the simulation approximates the true solutions to the differential equations of the original model. Validation, on the other hand, is said to be the process of determining whether the chosen model is a good enough representation of the real-world system for the purpose of the simulation. The literature on verification and validation from engineers and scientists is enormous and it is beginning to receive some attention from philosophers.