If you get curious, just read on. Introduction to Decomposition-based Motion Planning Motion planning is dealing with the problem of generating a motion for a robot so that a certain task is accomplished. We are all familiar with robots assembling cars and the problem of generating motion to accomplish such a task is pretty well understood. The assumption that all obstacles and their location are known at all times is a reasonable one. If we want to use robots in environments like hospitals, construction sites, and other populated places this assumption does not hold any more.
People move around, walls are built, material is unloaded and so on.
Most motion planning algorithms take a snapshot of the environment and determine a motion for this static description of reality. Since it takes them a significant amount of time to generate a motion, the environment might change even before the motion is computed. But even if we assume that it has not changed, the execution of a motion can take minutes or hours and during that period the environment has to remain unchanged for the motion to remain valid. If the environment changes, the precomputed motion might actually cause the robot to crash into an obstacle that has changed its location. This problem is particularly difficult to solve when the robot has many joints, also called degrees of freedom.