atial space 2.3.7 Integration Hierarchy The integration hierarchy is a predefined information structure for five model frag- ment types, see Fig. 2.44. Each type is said to exist on a particular integration level. The purpose of the integration hierarchy is to allow network functions to be mod- elled with decreasing levels of transparency. For example, when a service network is specified, the designer can disregard how service objects are accessed (by name, by identifiers, static, dynamic, etc.), how communication between service objects is realized (by procedure calls, messages, signals, etc.) and how to locate service objects in functional space (logical, physical or spatial addresses). An important property of the hierarchy is that higher levels are independent of lower levels. This is attained by specifying how a model on a higher level is integrated in a model on a lower level by separate integrates relations. An integrates relation defines which units of higher-level model fragments are contained in units on lower-level model 2 Foundations of Sysnet Modelling fragments. Note that the integrates relation strictly belongs to the lower level. Thereby, lower level models can be modified without affecting higher level models. For example, the structure and functional contents of the logical nodes of a logical network can be modified without affecting the specifications of service networks and abstract networks. The structure and functional contents of the physical nodes of a physical network can be modified without affecting the specifications of serv- ice networks, abstract networks, protocol networks and logical networks. Service networks: - access method transparent - transport service transparent - location transparent integrates Abstract networks: - transport service transparent - location transparent integrates Protocol networks: - location transparent integrates Logical networks: - physical location transparent integrates Physical networks: spatial location transparent Fig. 2.44 Model fragments in the int