ode. These modes are shown in Fig. 2.59 (compare with Fig. 2.37). 2 Foundations of Sysnet Modelling Perspective mode Flat mode Overlay mode Fig. 2.59 Visualization modes The perspective mode is intuitive, but difficult to support by a modelling tool. Most of us are not very good at producing perspective drawings. The flat mode means that a 3D-view is separated into a 2D-view and a 1D-view, and that relations between dimensions are visualized separately. This mode can easily be supported by a modelling tool, but it is not very intuitive and creates quite muddled models, even in rather simple cases. The overlay mode separates a 3D-model into a fore- ground model and one or several background models. This mode is intuitive enough and is the most practical mode to work with. The drawback is that not all relations between dimensions are visible, such as the platform service interfaces, in this case. Since you cannot "click" on these relations, the modelling tool must pro- vide special commands for accessing them. The views and visualization modes that are actually supported by a particular tool is an implementation matter. Principles of Graphical Notations in AML The expressiveness of graphical models is key to the success of any modelling 2.6 Principles of Graphical Notations in AML technique. The notational style offered by AML consists in part of predefined sym- bols and in part of notational principles, where the actual notation remains to be decided by users and tool makers. In the present chapter, the formal AML symbols are rarely used, but examples of some of them have been given. Examples include the symbols for network inter- face and service relation. In the remaining chapters, only correct AML symbols will be used. In this section, we only briefly discuss the notational principles used by AML. There are five types of model fragments that show collaboration structures: physical network, logical network, protocol network, abstract network and serv- ice network. For each type, the symbols for communication rel