AbstractClasses illustrated
- http://www.gnacademy.org/twiki/bin/view/CPP/AbstractClasses [BrokenLink 9-17-2009]
- http://www.gnacademy.org/twiki/bin/view/CPP/AbstractClassesAgain [BrokenLink 9-17-2009]
- http://msdn.microsoft.com/en-us/library/k535acbf.aspx
- http://www.javaworld.com/javaworld/javaqa/2001-04/03-qa-0420-abstract.html