n1.2.2 n1.2.1 n1.2.4 E (nw1.1) n1.2.5 nw1.2 Fig. 4.13 Node and network models on network level 1 The network level 2 view of a node structure in n1.2.1 is completely independ- ent of network level 1. According to Fig. 4.12 it looks like Fig. 4.14. n1.2.1 on network level 2: The logical-network structure in n1.2.1 (network level 2) n2.1.3 n1.2.1 n2.2.3 n2.1.5 nw2.1 nw2.1 nw1.2 n2.1.4 n2.2.3 n2.1.2 n2.2.2 n2.2.2 n2.1.3 n2.1.4 nw2.1 nw2.1 nw1.2 n2.1.2 (data, nw1.2origin.) n2.1.1 n2.2.1 n2.2.1 n2.1.5 hosts {...,ap1,. nw2.1 nw2.1 nw2.2 nw2.1 nw2.1/nw1.2 nw1.2 n2.1.1 E (nw1.1) Fig. 4.14 Node and network models on network level 2 4 Modeling Vertical and Horizontal Partitions A logical-network structure model that covers both network levels can be easily drawn by substituting the node n1.2.1 in the structure of Fig. 4.13 (to the right) with the structure in Fig. 4.14 (to the right), using the sub symbol to distinguish between levels. The result is the model in Fig. 4.15. hosts(h1) n1.4.10 n1.4.2 1.3.2 hosts(h2) n1.3.1 hosts n1.3.3 term(h1) term(h2) n1.2.1/nw2.2 n1.2.3 n1.2.6 n2.2.2 n1.2.2 n2.2.1 substructure n1.2.4 n2.2.3 n1.2.5 hosts n2.1.5 n2.1.4 n2.1.3 n2.1.2 n2.1.1 Fig. 4.15 The logical-network structure for the refined model, showing two adjacent network lev- els (through a sub relation). Vertical partitioning on network level 2 is defined through terminates relations This model reflects the fact that a model that covers both network level 1 and 2 is produced just by adding entities and relations to the original model. Thus, the modeling technique supports seamless refinement of a logical-network structure model over any number of network levels. As mentioned before, the fact that there is a sub relation between nodes n1.2.1 and n2.2.1 indicates that they belong to different network levels (no matter how nodes are named). A sub relation cannot, however, tell if the refinement implies vertical or horizontal partitioning. If we compare the models in Fig. 4.13 and 4.14, we see that the nodes n1.3.1 and n1.4.1 that are 