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Representation of temporal change in solid models

Solid models are static entities, usually defined by a boundary representation model as a set of enclosing surfaces. Constructive Solid Geometry and existing feature-based computer-aided design environments create procedural descriptions of 3D objects as history or CSG trees. These representations are temporally fixed, i.e., they describe the state of a 3D object at a particular point in time.
This paper describes a method to represent and capture the temporal evolution of solid models—what we call the model process history of an object. We define the process history to be the total set of states the model goes through during the design process—the search space of the detailed design process. This paper presents our work to develop a representational formalism we call model process graphs (MPGs). We use MPGs to integrate a traditional 3D solid model's BRep and feature-based descriptions with a model of the temporal changes that occur during the design process. We believe that MPG representations can have valuable application for many design and manufacturing problems. The paper briefly defines our MPGs that will (1) create a record of the design process; (2) store process-based design rationale; (3) represent in-process shapes for machined artifacts. We anticipate that MPG-like representations will find application in other design and manufacturing problems in which important process knowledge is embodied by temporal changes that occur as models evolve to their final forms.