A semantic network is a graph structure for representing knowledge in patterns of interconnected nodes and arcs. These structures can condense information about concepts or objects which might otherwise be scattered amongst many tables in a conventional relational database or buried in many pages of a scientific paper.
Minerva uses semantic networks to describe mineral deposits, deposit models or other exploration targets. Semantic networks are also used to describe locations on the ground, or underground, in terms of all available information.
For further details on semantic networks, you can read this article by John F. Sowa.