A connection represents a transfer of one commodity over space. For example, an electricity transmission line, a gas pipe, a river branch, can be modelled using a connection.

A connection always takes commodities from one or more nodes, and releases them to one or more (possibly the same) nodes. The former are specificed through the connection__from_node relationship, and the latter through connection__to_node. Every connection inherits the temporal and stochastic structures from the associated nodes. The model will generate connection_flow variables for every combination of connection, node, direction (from node or to node), time slice, and stochastic scenario, according to the above relationships.

The operation of the connection is specified through a number of parameter values. For example, the capacity of the connection, as the maximum amount of energy that can enter or leave it, is given by connection_capacity. The conversion ratio of input to output can be specified using any of fix_ratio_out_in_connection_flow, max_ratio_out_in_connection_flow, and min_ratio_out_in_connection_flow parameters in the connection__node__node relationship. The delay on a connection, as the time it takes for the energy to go from one end to the other, is given by connection_flow_delay.