Because newer phases such as 3-tier client/server and CBD essentially subsume the functionality of older ones, the migration of system is theoretically possible, although typically it is difficult due to the proprietary constructs of earlier products.

• 由于技术的新阶段基本上包含了旧阶段的功能，如三层客户机/服务器和CBD，所以在理论上系统的移植是可能的，虽然一般说来这种移植是困难的，因为以前的产品多为专有结构。