oduces a deeper level of structure in the applied system model. To keep standardized systems models separate from applied systems models is an important aspect of methodology, primarily because it supports tracing require- ments in case new requirements appear in standards (less frequent), or in case one wants to modify the applied system model for reasons that have nothing to do with modified standards (more frequent). In addition that the way standards are described cannot easily be synchronized with the way systems are described in a 1.4 Processing Systems manufacturer's organization, since we are talking of two very different develop- ment processes: the standardization process and the manufacturer's development process. Figure 1.4 shows the SM&AML-specific classification of system models we have discussed. Sysnet models standardized refines applied realizes implemented isAnInstanceOf concrete system system system system model model model model Fig. 1.4 A class diagram of system abstractions Read the relation realizes as: "an implemented system model describes how a manufacturer intends to realize a system that is described by an applied system model". Note that the class of system abstractions that are addressed by SM&AML are sysnets alone. Processing Systems In the world of all concrete systems of interest to systems engineering, processing systems is one of the largest, and is a very general set of systems. Telecommunica- tion networks and systems are very important parts of the infrastructure of our civ- ilization, and therefore an important subset of the set of processing systems. The goal of an information system is to store and manage data and to respond to questions. The information that such a system can provide to human users may be used to control some real-world process (e.g. income taxation). We can regard the combined system of the information system and the real world process that uses the information system as a processing system. The information system is, however, a more or less passive comp