Introduction This document is a part of the definition of a reference architecture for the integration of manufacturing software applications in the areas of design, fabrication and assembly of discrete electro-mechanical parts. The reference architecture is an element of the Systems Integration of Manufacturing Applications (SIMA) project at NIST (see Appendix A). The scope of the project, and therefore of the reference architecture, is limited to design engineering, manufacturing engineering, production systems engineering and production activities. Other aspects of the manufacturing enterprise, such as product planning, distribution and maintenance , are not within the scope of the project and are not included in the reference architecture. Following the definitiions in the SIMA Background Study [Bark95], we use the term reference architecture to mean: • the identification of types of systems that perform, or support human agents in performing, the activities within a given domain, and • the identification of the nature and content of the interfaces required among those systems. Accordingly, the reference architecture has three parts: • Part 1 — the Activity Model — provides a model of the generic activities involved in the manufacturing process, and the information flows required to support those activities. • Part 2 — the Systems Model — identifies the manufacturing application systems, both human and automated, which perform these activities, and the interfaces required for those systems to support the identified information flows. • Part 3 — the Information Models — define formally and in detail the objects and information which appear in the interfaces. This document is Part 1 — the Activity Model. It represents the first step toward the goal of the SIMA architecture project — to identify the functions and interfaces required of manufacturing applications software systems. It is intended to provide a frame of reference for SIMA projects and similar industrial projects, which are developing " standard interface specifications ". As a frame of reference, it permits such specification projects to name and " locate " the interfaces they intend to specify and assists those projects in defining the scope of those interface specifications, by identifying the functions the interface is intended to support. Companion documents will provide the other parts of the reference architecture and define a corresponding " engineering architecture " specifying for each interface the means of information exchange to be used and the representation forms for the information. Multiple engineering architectures which correspond to the …