MDX - Mechanism Design Extension - Provides engineers, within the product development process, kinematic motion simulation and behavioral insight into the assembly through the easy definition and animation of connections with Pro/ENGINEER, such as pin joints, ball joints and sliders. These connections, and resulting assembly constraints, facilitate the easy assembly of closed loop systems, like four bar linkages. These connections can be used compatibly and in combination with packaging and traditional Pro/ENGINEER constraints like mate, align and insert. MDO - Mechanism Dynamics Option - Adds dynamic functionality to Pro/ENGINEER Mechanism Design to provide a powerful virtual prototyping environment for the simulation and improvement of mechanism operation as part of the design process. Pro/ENGINEER Mechanism Dynamics allows designers to virtually engineer a mechanism without leaving the familiar user interface and workflow of Pro/ENGINEER.