In the implementing of STEP, the application protocol (AP) provides share model for specific domain, but it limits to operate each other.It is difficult to ensure its conformance and augmentability.

• 摘要在STEP应用过程中，由于现有应用协议的局限性，使得实现多个应用协议的操作变得困难，一致性得不到保证，也限制了对模型的扩展。