an expert system has as its base

an expert system has as its base

专家系统将所收集的专家的知识——那些专家用来做出决定的规则——作为该系统的基础。

　　as its base做宾语补足语，位置比较灵活，通常放在句子后面。本句由于宾语较长，所以把它提前放在谓语后面。如果宾语短的话，通常这样写：
　　An expert system has the collected knowledge of experts as its base。

　　the rules that experts use to arrive at decision. 由于the rules和knowledge of experts之间没有and，所以the rules看上去像knowledge of experts的同位语，之后that引导的是定语从句，修饰the rules。

An expert system has the collected knowledge of experts as its base, the rules that experts use to arrive at decision.
as its base只是提前了