SemWebGraphicalNotation

Here are some links to existing work

http://www.omg.org/spec/ODM/1.0/
http://webont.org/owled/2009/presentations/OWLED-KBBDW-v2.pdf
http://ceur-ws.org/Vol-614/owled2010_submission_5.pdf
https://www.oasis-open.org/committees/download.php/32174/owlvisualisation.pdf
http://www.researchgate.net/publication/226543059_UML_Style_Graphical_Notation_and_Editor_for_OWL_2
http://vowl.visualdataweb.org/v1/
http://www.essepuntato.it/graffoo

There are also software applications that support graphical notations:

http://thematix.com/tools/vom/
http://www.topquadrant.com/products/TB_Composer.html
http://protege.stanford.edu
http://www.knoodl.com/ui/groups/knoodl/wiki/Help/entry/Diagrams
http://owlgred.lumii.lv/
Sonivis Graph Visualization Ontology Plugin http://www.corporate-semantic-web.de/ontology-modularization-framework.html
SpecGen Visual Ontology Documentation Tool http://www.corporate-semantic-web.de/concept-grouping.html
Semtalk Ontology Editor - Microsoft Visio Modeling of Ontologies http://www.semtation.de/index.php/en/usecases-en/owl
http://mysite.verizon.net/jflynn12/VisioOWL/VisioOWL.htm
http://www.ihmc.us/groups/coe/
http://growl.novasemantics.it