1.3 Systems Engineering vs. Software Engineering

In many, if not most, real-time and embedded systems development, it is crucial to consider not only the software aspects, but also the system aspects. By systems aspects, we mean those aspects that affect the system as a whole, independent of the implementation technologies (e.g., software, electronic, mechanical, or chemical), as well as how these different design aspects collaborate. By systems engineering we mean the definition, specification, and high-level architecture of a system that is to be realized with multiple disciplines, typically including electrical, mechanical, software, and possibly chemical engineering. The primary activities encompassed by systems engineering include

• Capturing, specifying and validating the requirements of the system as a whole

• Specification of the high-level subsystem architecture

• Definition of the subsystem interfaces and functionality

• Mapping the system requirements onto the various subsystems

• Decomposing the subsystems into the various disciplines electronic, mechanical, software, and chemical and defining the abstract interfaces between those aspects

In all these activities, systems engineers are not concerned with the design of the discipline-specific aspects of the software or the electronics, but are concerned with the specification of what those design aspects must achieve and how they will collaborate.

The use of UML in systems engineering is increasing. A number of papers have been written on the topic (for examples, see [13,14]). The OMG has recently released a request for proposal (RFP) called "UML for Systems Engineering: Request for Proposal" [15]. At the time of this writing, work is underway creating a UML variant for this purpose.^[18] The current schedule calls for adoption of this language variant in mid-2004.

^[18] The author is a member of the SysML consortium working on this submission at the time of this writing.