 element can be modelled as consist- ing of an integrator and a number of service elements. On the lowest level of disintegration, protocol elements are disintegrated into a message-handling and an event-handling function. The latter is an implementation of an abstract machine. Cooperating abstract machines constitute an abstract network. Finally, an abstract network can be disintegrated into a number of service networks. The result of applying all four disintegration steps is that a sysnet model will consist of model fragments on five integration levels. Each level represents some degree of transpar- ency. The most transparent model type is the service network; the least transparent model type is the physical network. The structure of the five integration levels is called the integration hierarchy. Each of the five integration levels define their own concepts and symbols for com- munication relations, which are used to create model fragments on that level. The complexity of the individual model fragment that is created on each integration level is the modeller's choice. There are seven possible views for visualization of sysnet models, based on the D-, P- and C-dimensions. Views that comprise all three dimensions can be pro- duced by different methods, called visualization modes. Past experience has shown that the overlay mode is the most useful one. There are a number of AML-defined graphical symbols for communication rela- tions for different types of model fragments. Unit symbols are however normally defined by AML users or toolmakers. Other graphical notations are defined as prin- ciples only, since their actual form depends on the particular AML tool. 3 Logical Network Modelling Introduction The purpose of logical network modelling is to define the structure of logical nodes in functional space for a physical network. The model fragments that are created are logical networks, which belong to integration level 3 of the integration hierar- From a given logical structure of a network, there are many ways that 