I got a long stored procedure.

there are three parts

the first part
build a cursor
use the cursor to update the table

the second part
build a cursor
use the cursor to insert some record to the table

the third part
build a cursor
use the cursor to delete some records to the table

what confused me is that if there is errors happen on the third part of the store procedure, it seems to me my
first part (update ) is all undone, sort of rollback
but I never use the commit transcation and commit trascation
is this the way it supposed to be? is the default format for sql server store procedure is begin with beginTranscation and end with CommitTranscation?

anybody know that? Please tell me. Thanks a lot
and