Mapping product structures between CAD and PDM systems using UML

Abstract

The product data exchange between heterogeneous CAD and PDM systems is a crucial issue for the integration of product development systems. STEP offers an efficient mechanism of product data exchange between heterogeneous systems. This paper introduces a UML-based mapping methodology for the product data models. The suggested mapping method has been applied to exchange the product structure data between a CAD system and a PDM system. Based on the STEP methods, we developed an interface module.

Introduction

Manufacturing industry today faces challenges. In order to meet the competition in the market, the information technology has become one of the significant factors [5]. Early introduction of information technology applied computers to tasks previously carried out manually. For example, computer systems such as CAD (computer aided design), CAE (computer aided engineering), and CAM (computer aided manufacturing) have been successfully introduced and increased the productivity. However, the models of these computer systems are heterogeneous because they have been developed independently. The product data exchange between these automation systems becomes a crucial issue for the integration of product development systems. Recently the PDM (product data management) system is being used to integrate these systems into a common environment throughout the product lifecycle. The PDM system also has the problem of exchanging product data with legacy systems, especially with the CAD system that generates the product data. The interface between CAD and PDM systems is considered as an enabling technology for CE (concurrent engineering), CALS (commerce at light speed), and CIM (computer integrated manufacturing).

To integrate a CAD system with a PDM system, we need to develop a data translator. The mapping between the internal models of each system must be defined first. There are four different solutions for the data exchange problem; the manual re-input of data, direct translation, neutral format translation, and shared product database [5]. Each approach has its own pros and cons. Direct translation is the simple and accurate solution, but the number of translators increases exponentially with the number of systems involved. The last two solutions are reasonable, flexible, and adaptable. The product data exchange in this paper is based on STEP (standard for the exchange of product model data). Demartini et al. [4] presented a migration path to the STEP technology. Loffredo [14] studied an efficient database implementation of EXPRESS models. Zhang et al. [27] introduced a systematic approach to implement the interoperation between STEP APs (application protocols). Shin et al. [21] enhanced a ship design model using the STEP methodology and a non-manifold modeler. Hardwick et al. [8] studied sharing manufacturing information in a virtual enterprise. Bliznakov et al. [3] integrated a CAD system with engineering application programs in a distributed heterogeneous environment and proposed the information integration infrastructure based on an object-oriented multidatabase. PDMI2 (product data modelling on the basis of international standards) [19] project have developed a translator using the STEP PDM Schema.

Many different mapping methods such as EXPRESS-M [2], EXPRESS-V [7], EXPRESS-C, EXPRESS-X [1], XP-rules, and view mapping language have been proposed [26]. Liebich et al. [13] compared different approaches in this field. Hardwick et al. [9] proposed data protocols for a virtual enterprise using EXPRESS-X. The mapping methods can be classified into two types based on whether the models are homogeneous or heterogeneous. EXPRESS-X is a mapping language for the data described only in EXPRESS. Oh et al. [17] proposed a UML (unified modeling language) based mapping for the heterogeneous models. No one mapping method can be used in every situation, so the more flexible and general mapping methodology is needed, especially for the heterogeneous systems.

This paper discusses how CAD and PDM systems can be integrated using STEP standards in the product development environment. It is organized as follows: (1) STEP standards and their data structures are explained, (2) A mapping methodology based on UML is suggested for the mapping between heterogeneous systems, (3) The suggested mapping methodology is applied to the data exchange between a CAD system and a PDM system. Various types of integration between CAD and PDM systems are presented and (4) The STEP based interface of CAD and PDM systems is experimented with and implemented in an industrial field.