Research On STEP-based Information Integration For Virtual Enterprise

After an evolution of about 20 years, the standard for the exchange of product model data (STEP) developed by ISO TC184/SC4 has become a prevalent standard for the exchange of product data. The application scope of STEP has involved all aspects of the product life cycle. At the same time, the modern manufacturing technologies like virtual enterprise and parallel engineering have been adopted by industry for improving the response ability to the market and reducing the production cost. The research presented in this thesis describes the technology of information integration for distributed and heterogeneous systems using STEP, which is applicable for virtual enterprise applications. The primary contents are summarized as follows:An overview of the key functions of the EXPRESS modelling language as well as a formal semantic description of the EXPRESS data model is introduced. To deal with the coexistence of various data model in virtual enterprise applications, we presented a framework for the transformation of EXPRESS data model to multiple target models. With this framework, the techniques for transforming the EXPRESS data model to different target models, including object data model, relational data model and structured data model, are discussed.Based on the theory of isomorphism between EXPRESS data models, two kinds of model mapping techniques for STEP, i.e. the static mapping and the dynamic mapping, along with the implementation using EXPRESS-X mapping language are elaborated. With the help of the EXPRESS model mapping technique, we achieved the automatic generation of STEP data view and the interoperability among multiple application protocols.With the analysis of the basic requirements of data storage and access, we proposed that the information integration with data sharing is more suitable for virtual enterprise applications. Based on this conclusion, the architectures of STEP databases and their applicable scopes are discussed, as well as a SDAI C late binding system based on C/S architecture is presented for parallel and distributed access to STEP data. Three types of techniques for STEP data access on Internet are also studied with the comparison of their characteristics and applicable fields.The principle of the expression of feature model in STEP is elaborated. The form feature model in application protocols of AP214 and AP224 are studied, and the application of these two models in the fields of design and process planning are also discussed in the target systems of GS-CAD and GS-CAPP respectively. The application of these two models realized the exchange and sharing of information of form features in a part. We also discussed the distinction between the feature models in AP214 and AP224 and the related issues in model mapping.To meet the open nature of modern manufacturing systems, we designed and implemented the integrated STEP toolkit GS-STEP. A series of design principles for flexibility are adopted in the development of this system, with which we divide the function models of the whole system into three layers and implements them respectively, as well as improve the system independency of the tools. As a platform for information integration, GS-STEP has been applied in the GS-ICCC system successfully, which realized not only the data exchange between GS-ICCC and other CAx systems in open environment, but also the information integration of the subsystems like CAD/CAPP/PDM in GS-ICCC.