The modeling languages are of two types, those that are used in general purpose simulations and those that address specific areas and specific types of problems. The general purpose modeling languages deal with: interactive and non-interactive continuous systems, networks, queues, interactive and non-interactive discrete events, algebraic equations, ordinary and partial differential equations, distributed systems, linear and non-linear systems, and many-body systems. The simulation languages addressed to specific areas and specific types of problems are even more diverse than the general purpose languages. The specific areas and problems addressed include: factory operations, pipeline management, shovel-truck systems in open pit mining, gas and oil refining, fossil-fuel and nuclear power plants, missile system engagements, chemical processes, wastewater treatment, communications systems, computer systems, control systems, electronic circuits, and hydraulic systems. These also include transportation systems, social systems, economic systems, database analysis, street, utility line, and stream networks, mass and energy balance, energy optimization, thermodynamics, pharmacokinetics, respiratory physiology, cardiovascular physiology, robot design, and robot dynamics.