Ontology visualization tools serve the expanding needs of knowledge engineering communities. A number of visualization frameworks for the standard ontology language OWL have already been developed. Considering information visualization in general, we propose the criteria of simplicity and completeness with which to gauge ontology visualization models. After analyzing existing OWL visualization frameworks we propose a simple visualization model for OWL-DL that is optimized according to our criteria. This visualization model is based around the underlying DL semantics of OWL ontologies; it circumvents the perplexities of RDF syntax. It has been implemented in GrOWL- graphical browser and editor for OWL ontologies. We discuss the usage of GrOWL in Ecosystem Services Database.