在The news that we are going to the United States is not true.一句中that引导的从句部分被确认为同位语从句,但我认为可以看作是定语从句.请问,定语从句和同位语从句有什么严格的区别吗?
请指教

成分上的区别：
    名词从句和定语从句分别在句中充当什么样的成分？
1. How the prisoner escaped remains a mystery.主语
2. I wonder whether/if he is fit for the job.宾语
3. The problem is who will be equal to the task.表语
4. He had no idea whether we could overcome the present difficulties or not.同位语

下面5--8都是作定语的。（定语从句）
5. I visited the country which/that had been bombed by the US-led NATO (美国为首的北约) a month before．
6. I shall never forget the years when I lived in the countryside with the farmers, which  has a great effect on my life.
7. In the office I never seem to have time until after 5:30 pm., by which time many people have gone home.
8. I had never seen such a good film as I watched lastnight.

结论一：    名词从句充当句子的主要成分（主、宾、表、同）；

            定语从句充当句子的修饰成分。（定）

引导词含义上的区别：引导词是否指向句中的某个成分？
1. That he came back made us very happy.
5. He made another wonderful discovery, which
  I think is of great importance to science.
6. Kennedy and Johnson, both of whom were
  murdered in their terms, once co-worked as
  president and vice-president．
7. The Oscar is one of the film prizes that have
  not been offered to any Chinese actor or actress
  by far．
8. The Oscar is the only one of the film prizes 
  that has not been offered to any Chinese actor
  or actress by far．

2. I’m sorry (that) I’ve made a mistake.
3. The fact is that his bark is worse than his bite.
4. Word came that he would come to see us all.
9.  The days are gone forever when we used
  foreign oil.
10. As  we all know, China is a developing country.
11. This is the village where my father once lived
      for several years.
12. 1980, when Chinese government began its
      reform, is an important year for China.
结论二：定语从句的引导词在语义上具有指代先行词的作用。

  名词从句的引导词不具备此功能。

关于that:  that 在名词从句和定语从句中各起什么作用？
1.He pretended (that) he didn’t see me.
2.That she lost her necklace on the way home made her so worried.
3The news that Tom won the game made us excited.
4The reason why he came late was that it was raining .

问题：that 作何成分？

5.The school that my sister studies at is far from here.(which)
6.The first request that he made was to ask for freedom.
7.It was said that that was all that he said.
8.Is this the house that you have bought yourself?(which)

结论三：

名词从句中的 that 只起引导词的作用，无任何意义。

定语从句中的that 在从句中充当主语或宾语，有时可以与 which 互换。

引导词的不同：
  不会出现在名词从句中的关系词：as
注意：when, where在名词性从句中 等不能与 in/on/at which 互换。
不会出现在定语从句中的关系词：whether, if, what, how,as if