An Ontology of Mechanical Devices
Thomas F. Stahovich, Randall Davis, Howard E. Shrobe · 1998
pulleys, flywheels, cranks, sprockets, and other powertransmission elements." By this definition, nearly every mechanical component is a shaft. This is a widespread phenomenon: text books uniformly assume that the basic definitions are so obvious that no explanation is needed. While people do indeed have informal, tacit understanding of terms like clutch and lever, making those definitions sufficiently explicit and accurate for machine use turns out to be interestingly challenging. We have spent a surprising amount of time getting even very basic concepts suitably refined. Consider, for example, one of the most primitive mechanical devices, a lever. The term is sufficiently familiar that the definition would seem trivial. One obvious answer is "a rigid bar with a pivot." Figure 1 is a simple example showing some of the subtlety of getting the definition right: the pivot is on the left, there is a weight at the right, and a stack of blocks in the middle. By the definition given, this