Each model is composed of one or more model versions. Usually, a modeler attempts to describe the complete set of simulations through parameter manipulation. However, in many instances, it is likely that new and novel interventions will not be anticipated by the code developer. In these instances, it is common for the developer to create a different version of the model to handle a subset of the simulated interventions. One of the explicit objectives of the MREP is to track the different model versions and to link them to the results they produce.