Nowadays , the model of database system has been developed very vell and almost all aspects of DBMS have been very successful .

如今关系数据库理论模型已经近乎完美，而且各种关系数据库系统几乎在各个方面都非常成功。

The author presents the construction of type ZG-70 semiautomatic tube expander and its function . This tube expander has the advantages of simple costruction , easy fabrication , flexible operation and reliable expanding quality . During several years of operation this tube expander is proved to be good in performance and has been vell accepted by workers .

本文介绍了ZG-70半自动胀管机的结构和动作原理，该胀管机具有结构简单、制造方便、操作灵活、胀管质量稳定等优点，经过几年的应用证明其性能良好，深受工人的欢迎。