Offline and online operations

Today, Internet users have asked to see what is off-line operation, what is the online operation.
Offline operation: read all the operation data, and then treated in one portion.
Online operation: each read operation data, perform one operation.
It is noteworthy that the two are not equivalent to, sometimes, offline than online operation faster.
However, the disadvantage of off-line operation is also very obvious. That is to take up some extra space.

Dynamic segment tree can be a prescription, but when discrete data processing needs, you need offline operation, under normal circumstances, a great need discrete data when the card will not be off-line operation.