redirection and pipeline

I was wondering about differences and relation between redirection and pipeline.

1. Is pipeline only used to connect
stdout output of a command to stdin
input of another command?

2. Is redirection only used to connect
a stdout output of a command to a
file, and to connect a file to a
stdin input of a command? But there
seems to be command >& 2.

3. A pipeline com1 | com2 can be
replaced by redirection as com1 >
tempfile; com2 < tempfile. Can the
replacement be modified to be
without using a file?

4. Can a redirection be replaced by a
pipeline?

Thanks and regards!