order of database modifications in a single transaction

Can it be assumed that the database will try to commit all the updates,
deletes, and inserts in the order they are submitted during a single
transaction for the sake of planning trigger firing order? In the
following scenarios?

    A/ From within a procedure run from the command shell or a external
script.
    B/ From withing a procedure from the command line.
    C/ with Autocommit off and within Begin and end blocks of a
transaction.

Is this a general assumption possible with all transaction supporting
databases, that at the moment of commitment a single transaction, the
database modifications in that transactions will be popped from a queue
FIFO and committed individually in order?

Also, when one transaction is committing does it own that bottleneck
blocking other transactions from committing until the whole queue of DB
modifications in the current committing transaction are done? I.E. it
gets a semaphore for the commitment functionality? ( I guess I could
have worded that to say, is the commitment phase of a transaction atomic
relative to other pending transactions? )
--

Carpe Dancem ;-)
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Remember your friends while they are alive
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                         Sincerely, Dennis Gearon