The paper first gives the formal definition of TU model, t hen study and analyse TU model by instance deeply, and gives the advan tage and disadvantage, on the base of that, the paper suggests an idea studying TU model next.

• 给出了tu模式的形式化定义，并结合实例对该模式进行了深入的分析和研究，指出了其优缺点，并提出了对该模式的下一步研究思想。