This paper studies tree pattern minimization in the presence of DTD.The SC to ESC that can express descendant relationships under DTD constraints is extend.

• 重点讨论DTD约束下树模式的最小化问题，将DTD兄弟约束SC拓展成扩展兄弟约束ESC，使其能够表达DTD约束中的祖先-后代关系；