It is increasingly important for organizations to achieve additional coordination of diverse computerized operations. To do so, it is necessary to have database systems that can operate over a distributed network and can encompass a heterogeneous mix of computers, operating systems, communications links, and local database management systems. This paper outlines approaches to various aspects of heterogeneous distributed data management and describes the characteristics and architectures of seven existing heterogeneous distributed database systems developed for production use. The objective is a survey of the state of the art in systems targeted for production environments as opposed to research prototypes.

• 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 reference architecture, but use different mechanisms or forms for interchange, are possible.

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While developing software systems, and during the enterprise's subsequent evolution, developers define models. These models can help automate some systems integration tasks. The joint action model describes a new business transaction that motivates systems integration.

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