Simulation and modeling - Old Questions

Verification is the process of determining that a model implementation and its associated data accurately represent the developer's conceptual description and specifications.  Verification answers the question "Have we built the model right?". The verification focuses on comparing the elements of a simulation model of the system with the description of what the requirements and capabilities of the model were to be. Verification is an iterative process aimed at determining whether the product of each step in the development of the simulation model fulfills all the requirements levied on it by the previous step and is internally complete, consistent, and correct enough to support the next phase.

Validation is the process of determining the degree to which a simulation model and its associated data are an accurate representation of the real world from the perspective of the intended uses of the model. Validation answers the question "Have we built the right model?”. The validation focuses on the agreement between the observed behavior of elements of a system with the corresponding elements of a simulation model of the system and on determining whether the differences are acceptable given the intended use of the model. If a satisfactory agreement is not obtained, the model is adjusted to bring it in closer agreement with the observed behavior of the actual system (or errors in observation/experimentation or reference models/analyses are identified and rectified).