change the abstract protocol (and thereby the abstract network), but not the service network. A service network can be expected to be considerably simpler than the abstract network of which it is a part. A service network can often be designed to corre- spond to a particular service or service feature that is provided by the telecom sys- tem to its users. 2.3.8 Concepts Summary If we add functional space, the integration hierarchy and substructuring, we have five dimensions in which sysnets can be described. Three of the dimensions define functional space, the fourth dimension is the integration hierarchy and the fifth is the hierarchical structure of models that can be constructed within an integration level by applying substructuring. Components of concrete systems have properties in all or most of the five dimensions, which indicates their complexity. The ration- ale for defining five dimensions is to simplify modelling and specification by iden- tifying units and communication relations that can be described in one or a few dimensions at a time. In this section, we will therefore summarize all major con- cepts, separated into semantic diagrams based (primarily) on the three dimensions in functional space. A semantic diagram defines concepts and relations between concepts. Concepts are denoted as textstrings, and the relations by arrows. Symbols for relations are the same as are used for resource system modelling, see Sect. 7.1. Applying functional space implies that units of type node network function, log- ical node and protocol element can be viewed in any of the three dimensions D, C and P (similar to the node network function in Fig. 2.35). Abstract machines and service objects are exceptions, since these units and networks are defined inde- pendently of where they appear in functional space (which first becomes defined+ when abstract machines are integrated in protocol elements, protocol elements in logical nodes, etc.). The semantic diagram for service networks and abstract net- works is described in Fi