To produce accurate system architecture descriptions, it is essential to be able to describe interfaces between system elements at different levels of abstraction and from different perspectives at the same time. For example, the connection from system A to system B may be viewed at a high level as independent of the mechanisms that implement that flow (copper wire, free space RF, optical), and it may be useful to explore which of several of these mechanisms might be used. It is also frequently useful to analyze and constrain the problem (interface bindings) at several levels of detail (application protocols, network protocols, physical layer connections) separately, as well as in combination.

A well-known conceptual model from the world of information systems was used here — the Open Systems Interconnection Basic Reference Model (OSI-BRM). A method was devised to concisely represent this conceptual model, and abstract, functional, interface, and protocol realizations using UML/SysML. The pattern that was developed for modeling system interfaces provides an MBSE method that can be directly applied to systems interfaces. And there is a general-purpose extension of this method that has a wide range of potential applications in other domains. The method leverages the well-established descriptions of layered system interfaces from the OSI-BRM, in conjunction with model-based systems engineering and the analysis of stakeholders, concerns, views, and viewpoints as described in ISO 42010 and the Reference Architecture for Space Data Systems (RASDS, CCSDS 311.0-M-1).

The primary value of this novel modeling pattern is to allow complex system and interface interactions to be decomposed and represented in a consistent way. System interfaces may be modeled at a high level and then, as needed, modeled at deeper levels of specificity, until tied to particular protocol specifications at each layer and even to end-to-end behaviors as needed. A set of views and viewpoints is described that can be used to express system element connections, behaviors, and constraints at successively deeper levels of detail.

A future goal is to extend and apply this pattern to other domains of engineering and system engineering to address the increasing complexity and number of interfaces that system engineers must manage for today’s projects.

This work was done by Peter M. Shames and Marc A. Sarrel of Caltech for NASA’s Jet Propulsion Laboratory. This software is available for license through the Jet Propulsion Laboratory, and you may request a license at: here . NPO-49390

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This article first appeared in the October, 2017 issue of Tech Briefs Magazine.

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