Fact Guru's Object Oriented Knowledge Base is a comprehensive knowledge base of terms and concepts related to object-oriented software engineering. Based on the book "Object Oriented Software Engineering: Practical Software Development using UML and Java (from amazon)".
The "subjects are arranged in a hierarchy - each subject "is a" kind of the subject above it. You can also view the subjects in alphabetical order or as a graph. If you click on a subject in the hierarchy, you will see facts about that subject appear in this pane. From there you can follow links to other subject. You can compare a subject and its siblings, or all the children of a subject by clicking on the Compare tab."