data item z reads the value thereof and releases the lock on it table 8 representing a history file of data item z shows that transaction c has written to data item z prior to transaction a 39 s read step therefore transaction a is dependent on transaction c in transaction serialization graph 20 a third directed edge 26 is added from node 21 to node 23 showing this dependency as graph 20 is searched for presence of cycles it is determined that a path exists from transaction a to transaction c to transaction b and back to transaction a therefore transaction serialization graph 20 is a cyclic graph where a cycle of dependencies exists since transactions a b and c in the cycle of graph 20 depend on each other 39 s results the transactions are not serializable in order to achieve serializable execution of all transactions in a transaction serialization graph each transaction in the cycle and its dependent transactions must be aborted and rerun therefore transactions a b and c must be aborted and restarted as shown in table 5 in order to prevent the repeated formation of a cycle in a transaction serialization graph by the rerun transactions the restarted transactions should.