怎样判断独立主格结构那怎样与定于从句区分呢

怎样判断独立主格结构
那怎样与定于从句区分呢

我个人理解,独立主格,就是把谓语动词变成-ing形式,doing的形式不是谓语了,没有谓语也就不是一个句子了.
eg：There being no taxis,we had to walk.没有出租车,我们只好步行.
这里只有一个句子,就是we had to walk.而前面的There being no taxis不是句子,是we had to walk的原因.
定语从句的话,首先他就是个句子了,一个句子作定语.把上面这句话变成 定语从句的话,就是there were no taxis,because of which we had to walk.
一般说,独立主格和定语从句的区分还是很容易的,但是有时候 其他一些从句和定语从句的区分就不是那么显而易见了.