The Visual Notation for OWL ontologies (VOWL - pronounced "vowel" [vou-uh l]) provides graphical representations for elements of the Web Ontology Language (OWL). It allows for an integrated view on ontologies that visualizes classes (circles) along with their individuals (sections in the circles) and property relations (connecting lines and arrows).
[VORLESUNG: ...just for info, not mandatory]
Ian Horrocks, Peter F. Patel-Schneider, and Frank van Harmelen. From SHIQ and RDF to OWL: The Making of a Web Ontology Language. J. of Web Semantics, 1(1):7-26, 2003.