doesn't seem to have been 是什么句型，请教我用法谢谢。

Question

If we are talking about violent crimes, there doesn’t seem to have been much change, but many property crimes, like burglary have certainly decreased because home security is much better than before.

Answer 1

回答如下：
分三个方面回答：
1. 在there be句型中，除了be动词之外，还可以是seem，appear，come , stand, happen, exist，live等动词，并且这些动词可有时态变化，这些都是there be句型的变体。例如：
There seems to be a mouse in the room.
There used to be a tree here.
There appears to be nobody who wants to go.
There happened to be a train going to Beijing.
There lived an old man long long ago.
Just then there came a knock at the door.
2. seem的否定有两种：用do / does / did not 或者否定后面的不定式：
He seems not to know it.
或者：He doesn't seem to know it.
3. 英语不定式有三种形式：
一般式(不定式与谓语的动作同时发生，或谓语动作先于不定式动作。)：
He seems to know it.
We want to go there.
完成式(不定式动作先于谓语动作)：
He seems to have known it yesterday.
进行式(不定式与谓语动作同时发生，强调正在进行。)：
She seems to be sleeping now.

Answer 2

there seems 是there be句型的变体，to have been是不定式的完成式，表示这个动词发生时间较早，在谓语动词之前。