Systems engineering has been plagued by the problem of how to separate a system from its environment or context, in particular from its social context. We propose to include anything in the system that is necessary for performing its intended function and that may be the object of design. For certain engineering systems, such as civil aviation systems, this implies that human agents and social institutions have to be taken as integral parts of these systems. These 'socio-technical' systems are of a hybrid nature because they are constituted by different kinds of elements, intentional and nonintentional: social institutions, human agents and technical artefacts. This paper analyses two different roles that human agents, as elements of socio-technical systems, may play with regard to technical artefacts. Furthermore, it discusses some conceptual problems concerning the modelling of socio-technical systems that are due to the hybrid nature of these systems. *

The conceptualization of the notion of a system in systems engineering, as exemplified in, for instance, the engineering standard IEEE Std 1220-1998, is problematic when applied to the design of socio-technical systems. This is argued using Intelligent Transportation Systems as an example. A preliminary conceptualization of socio-technical systems is introduced which includes technical and social elements and actors, as well as four kinds of relations. Current systems engineering practice incorporates technical elements and actors in the system but sees social elements exclusively as contextual. When designing socio-technical systems, however, social elements and the corresponding relations must also be considered as belonging to the system.

Abstract. In this paper we discuss how the increasing importance of socio-technical systems affects systems engineering. We start with a clarification of the notion of systems engineering by distinguishing two ways in which engineering design is involved with systems characteristics: in the object of design and in the design approach. Next we focus on system-like objects of design of a special sort: socio-technical systems. After presenting two examples, we indicate several tensions between the systems engineering design approach and the design of socio-technical systems.

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