关系模型基于谓词逻辑和集合论，为数据库管理提供了坚实的数学基础。

The best diplomat is one who can see the trends of future developments, not just the realities of the present.

We Germans will never get rid of Hitler. He is like a birthmark on our face.

发现的快乐无疑是推动科学前进的动力。