A method of comparing two object poses, wherein each object pose is expressed in terms of position, orientation and scale with respect to a common coordinate system, the method comprising:calculating a distance between the two object poses, the distance being calculated using the distance function:dsRt\u2061=ds2\u2061\u03c3s2+dr2\u2061\u03c3r2+dt2\u2061\u03c3t2. Utilizing this in-memory representation, a class in one form is automatically generated and customized wherein this class is used to access a hierarchical database responsive to a hierarchical database access request from an application. A piston is disposed in the piston chamber.