Dr. Stonebraker has also provided a way for classifying DBMSs based on performance on complex data. He mentioned this during a question and answer session at the Object/Relational Summit in Boston in August, 1997. He said, "My point of view is that if you want to navigate your objects in C++, object databases do that blindingly fast -- way faster than a relational or an object-relational engine." (This was before Java became popular.) Listen to Dr. Stonebraker: Stonebraker.mp3.
Let's look at what it means to navigate objects. The following figure shows a few instance objects that are part of a database of parents, children, and addresses. The arrows show the relationships among the instance objects. Moving from one instance to another along the arrows is navigation. Languages such as C++ and Java provide ways to navigate among objects. The speed of this navigation is what Dr. Stonebraker describes as the strength of ODBMSs.
More on the general topic: Stonebraker's DBMS Matrix