I. Summary This paper searches for a useful taxonomy or classification scheme for complex Systems. There are two aspects to this problem: 1) distinguishing between Engineering Systems of interest to ESD (ES) and other Systems, and 2) differentiating among Engineering Systems. The first of these has been approached through general interaction with other ESD faculty and use of the ESD definitions. This analysis leads to a proposed specific set of ES which are human designed, have high technical

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... d human complexity and are real, open, dynamic, have hybrid system states and have both autonomous and human-in-the loop subsystems or elements. The second aspect has been approached by top-down and bottom-up analysis. A topdown approach consists of reviewing past system classification schemes starting with taxonomies proposed in the context of General Systems Theory from the 1950's and assessing their usefulness with the proposed list of ES. Such schemes prove to be of limited value in our search because they tended to be formulated from a mechanical technology viewpoint and more importantly because they could not anticipate the emphasis herein on systems with both technical and human complexity. The proposed or testbed list is also useful in the bottom-up approach, since it gives specific cases for qualitative and quantitative analysis of various system attributes. The qualitative and preliminary quantitative study indicates that functional types are the most useful technical attribute for classification differentiation. Information, energy, value and mass acted upon by various processes are the foundation of the technical types building on prior work by Hubka, Pahl and Beitz and Van Wyk. A meta-model for Engineering Systems is suggested in the form of a multi-layer network whose goal it is to fulfill human wants and needs by enabling the flow of goods and services between sources and sinks. This description essentially combines and extends the attributes suggested by the bottom-up approach to be most useful in classification.