The STEP Modular Architecture Allison Barnard Feeney National Institute of Standards and Technology, 100 Bureau Drive, Stop 8264, Gaithersburg, MD 20899-8264 e-mail: abf@nist.gov Abstract The first Technical Note in this series [1] introduced the international standard ISO 10303, informally known as STEP (STandard for the Exchange of Product model data). Subsequent Technical Notes discussed various issues faced by users of STEP and how the ISO TC184/SC4 committee is addressing these issues. This paper presents the current move to modularize the STEP application protocol architecture. This paper describes the initial STEP architecture, requirements for improvements to the architecture, features of the new modular architecture, status and issues. Background STEP (STandard for the Exchange of Product model data, formally known as ISO 10303) is an international standard designed to enable the exchange of product data between heterogeneous computer systems used throughout the product life cycle. STEP is being developed under the leadership of ISO TC 184/SC4, the ISO sub-committee responsible for data exchange standards in the area of industrial and manufacturing applications [2,3]. A new modular STEP architecture addresses some deficiencies of the original architecture and is intended to speed development, facilitate implementation, and increase interoperability of applications of STEP. This paper introduces the new modular architecture in the context of the initial architecture. First, the initial STEP architecture is described. Requirements governing the development of the modular architecture are summarized. Components of the new modular architecture are presented with an explanation of how the initial architecture is changed. The current status of the modularization effort is presented, followed by issues that remain to be addressed. Initial STEP Architecture The architecture of STEP is designed to support the development of standards for product data exchange and product data sharing [4]. The architecture is governed by the following concepts: (1) the scope of what is standardized and what is conformance tested is set at the level of “an application,” (2) application requirements are based on a model of a business activity, (3) application requirements are standardized using natural language, and (4) a mapping is specified defining how the application requirements are satisfied using a STEP data model [5]. The key information models comprising the STEP standards are known as application protocols (APs). As illustrated in Fig. 1, an AP consists of the following major elements: