Conceptual graphs (CGs) are a formalism for knowledge representation. In the first published paper on CGs, John F. Sowa (Sowa 1976) used them to represent the conceptual schemas used in database systems. The first book on CGs (Sowa 1984) applied them to a wide range of topics in artificial intelligence, computer science, and cognitive science.
via Conceptual graph – Wikipedia
Well worth taking a look at Conceptual Graphs — in large part, Kyndi’s (http://kyndi.com) technology uses conceptual graphs as one of the pillars for natural language understanding.