As companies strive to advance their modeling and simulation capabilities toward realizing full virtual prototypes of aircraft systems, they face a number of challenges associated with assembling multi-domain system models. Beyond the inherent time and budget pressures, they interact and collaborate with a variety of departments, suppliers, and manufacturers as a source of models, they must deal with a diverse mixture of tools, modeling formats and conventions of different domains, and they must preserve and repurpose an often decades-old legacy of modeling knowledge and assets.