<database> A technique for maintaining integrity in
distributed databases. Where a system uses two or more
database, a transaction among the distibuted database should
be atomic ("all or nothing"). This is done by handling the
transaction in two phases. First the databases prepare the
transaction, confirm that it is possible to process it, and
lock the relevant record.
Once all the required databases confirm that the transaction
is viable, the system instructs them all to commit it -
i.e. to make it permanent. If it is not possible to process
it, the system will instruct the databases to rollback
(undo) the transaction.
