如何判断定语从句和同位语从句

判断的依据是看所修饰的词在后面的从句中充不充当句子成分
I've got the news when the film will be on show,后面的句子whenthe film will be on show中成分完整,所以是同位语从句.
The building which stands near the river is our school中building在后面的句子stands near the river is our school中充当主语成分啊这就是定语从句