g cluster_0 graphical schematics sheet cluster_01 drawing primitives (chapter 3) cluster_02 concrete model (chapter2) cluster_1 abstract model (chapter 2) cluster_2 real world example: PCB at1 "bus-segment": atoms, e.g. lines gr1 group role=bus-net at1->gr1 at2 "wire-segment": atoms, e.g. lines gr2 group role=wire-net at2->gr2 at3 atoms and groups gr3 group role=symbol at3->gr3 at4 atoms e.g. lines gr4 group role=bus_terminal at4->gr4 at5 atoms e.g. lines gr5 group role=terminal at5->gr5 at6 atoms e.g. arc, polygon gr6 group role=hub_point at6->gr6 at7 connection gfx e.g. arc, polygon connection connection at7->connection bus_net bus-net gr1->bus_net wire_net wire-net gr2->wire_net symbol symbol gr3->symbol bus_terminal bus-terminal gr4->bus_terminal terminal terminal gr5->terminal hub_point hub-point gr6->hub_point connection->wire_net Note 2 connection->bus_net Note 2 attribute attribute of wire-nets, bus-nets, symbols, hubs and terminals symbol:e->attribute:se component component symbol->component terminal:e->attribute:se port port terminal->port bus_terminal:e->attribute:se bus_port bus-port bus_terminal->bus_port wire_net:e->attribute:se network network wire_net->network hub hub hub_point->hub bus_net:e->attribute:se bus bus bus_net->bus attribute->network Note 1 pcb_net copper tracks copper polygons network->pcb_net bus->pcb_net pcb_pair copper tracks/polygons with constraints (e.g. diff pair) bus->pcb_pair pcb_component component component->pcb_component pcb_pin pin or pad of a component port->pcb_pin bus_port->pcb_pin hub->pcb_net pcb_hub specific point on copper with geometry constraints (e.g. star point gnd) hub->pcb_hub