EXPERIMENTAL INVESTIGATION OF THE STEP FORM-FEATURE INFORMATION MODEL

Exchanging product data between feature-based geometric modelers presents some challenges. This is partly because features technology is still evolving, and also because there are major philosophical differences between the feature concepts on which different systems are based. The Form Feature Information Model (FFIM) that was developed by the PDES committee in the USA and accepted into the International Standards Organisation STEP standard was tested by means of experiments described in the paper. The modeler used in the experiments was the ASU Features Testbed, which was developed at the Arizona State University, USA, independently of the FFIM. The purpose of the experiments was to identify problems in the FFIM, and to suggest solutions where possible. In addition to the traditional problems of data transfer, such as numerical inaccuracies, a number of other factors that increase the complexity of the feature data-exchange process were identified. Some of these were the lack of relational positioning/locating information, multiple representations of a single feature, representation of certain popular profiles in rather tedious data structures, and the nonunique mapping of features between the two systems. The loss of semantic information, ecapsulated in rules, methods and constraints, seems to place some serious limits on information that can be exchanged with the current version of the FFIM. The PDES/STEP models are essentially static snapshots that are adequate for exchanging geometric and topological data, but are insufficient for dynamic exchange of feature models that encode engineering semantics in addition to geometric shapes.