Features, aka the semantics of a formal language of manufacturing

Features are application and viewer-dependent interpretations of geometry. This article demonstrates how the notion of features arising out of geometric data may be formalised as the semantics of a language of shape, using machining operations as an extended example. The syntax and semantics of formal languages are discussed, with particular reference to their use in design. A simplified lathe is defined, and a parametric attributed set grammar is presented which specifies the range of shapes manufacturable on that lathe. A simple feature space is then defined, in which feature models representing those shapes may be constructed. The link between the shapes and the feature models is then formalised as the semantics of the grammar using description functions, and it is shown how the feature models develop as shape generation proceeds. Finally, some implications of this work for feature-based design and manufacturing are discussed.