A Software Component which is intended to carry out a narrow, well-defined function such as the computation of physical properties, the simulation of a particular unit operation, or the numerical solution of certain types of mathematical problems arising in process simulation or optimization. This is a process element such as a unit operation, a numerical solver, a thermodynamic server, a physical property data base, etc. Examples are heat exchanger design models, pump models, distillation models (including packing, distributor, or tray models), hydrocarbon cracker furnace models, mixer/agitator calculators, safety relief design calculators, fluid flow network calculators, non conventional unit operation models.