<xsd:documentation>A pointer to the network containing the unit that this network represents.
That is, the Unit must exist in a different Network.
If a parent network is not specified then the network represents the model.
A model should only be represented by one network.
The model network represents the overall installation.
All other networks represent internal detail and should not be referenced from
outside the model. The external ports on the model network represent
the external ports to the overall Product Flow Model.
A pointer to an external port on the Product Flow Model does not require the name
of the model network because it is redundant to knowledge of the model name
(i.e., there is a one-to-one correspondence).</xsd:documentation>