his is an abstract language for message specification. In AML we use ASN. 1, with some minor modifications, as the basis for data specification in gen- eral and message specification in specific. How messages and message handling are specified by using SM&AML is describe in more detail in Chap. 5. Abstract protocols and primitive services focus on the meaning of message information and describe the communication behaviour between parties (abstract machines and service objects respectively) that communicate by communication events that refer to operations. The operations defined in an abstract protocol can be grouped into subsets that refer to service objects that collaborate over service relations, each service relation defining one primitive service. AML supports a technique for specifying abstract protocols and primitive services in an implemen- tation-free way that has its roots partly in ASN.1 and partly in the Remote Opera- tion Service Element (ROSE) standard, described by ITU-T in recommendations ITU-T X.219 and X.229. The ROSE technique is, however, considerably improved in SM&AML. Views and Visualization Modes The definition of functional space implies that logical networks and nodes have a three-dimensional logical structure. Through the orthogonal qualities of the dimen- sions, functional space is well suited for creating and viewing a physical network in just one or two dimensions. This modelling method not only suits humans better, but also simplifies the design of tools for model visualization and editing. By the introduction of functional space, we can identify the seven views that can be cre- ated: DPC, DP, DC, PC, D, P and C. For example, a D-view might look as the model we discussed in Fig. 2.37. One- or two-dimensional views are mostly sufficient for sysnet modelling, but there are occasions when one wants to work with, or just see the model in all three dimensions. There are, in principle, three methods that can be used, called visuali- zation modes: The perspective, the flat and the overlay m