1 TRANSACTION CONTROL EXPRESSIONS (TCEs) Ravi Sandhu

2 OUTLINE Transactions Transaction sagas Transaction control expressions (TCEs) Transient versus persistent objects Automated transaction sagas

3 TRANSACTIONS DATABASE TRANSACTIONS Data abstraction and internal consistency USERS

4 TRANSACTIONS Abstract operations –credit, debit Serializability –interleaved execution is equivalent to a serial execution Failure atomicity –either all or none of the actions of a transaction actually take effect

5 TRANSACTION SAGAS 1. A clerk prepares the voucher 2. The voucher is approved by a supervisor 3. A clerk issues the check

6 TRANSACTION CONTROL EXPRESSIONS (TCEs) prepare clerk; approve supervisor; issue clerk; prepare Alice; approve supervisor; issue clerk; prepare Alice; approve Bob; issue clerk; prepare Alice; approve Bob; issue Carl;

7 TCEs Dynamic separation of duties Hierarchical roles Substitution of attribution

8 HIERARCHICAL ROLES Supervisor Clerk Purchasing Clerk Receiving Clerk

9 VOTING prepare clerk; 3: approve supervisor; issue clerk; prepare clerk; 3: approve supervisor=1, manager=2; issue clerk;

10 VALUE BASED APPROVAL prepare clerk; if value > 1000 then3: approve supervisor else 1: approve supervisor; issue clerk;

11 MULTIPLE APPROVAL publish scientist; approve security-officer & approve patent-officer; release librarian;

12 ANCHORS requisition project-manager ; prepare clerk; agree project-manager ; approve purchasing-manager; issue clerk;

13 TRANSIENT vs PERSISTENT OBJECTS 1. A clerk prepares the voucher and assigns an account 2. The voucher and account are approved by a supervisor 3.A clerk issues the check debiting the account as a side effect –Voucher -- transient object –Account -- persistent object

14 TRANSIENT vs PERSISTENT OBJECTS Transactions are executed on persistent objects only as a side-effect of executing transactions on transient objects

15 TRANSIENT vs PERSISTENT OBJECTS TRANSACTIONS Data abstraction and internal consistency USERS PERSISTENT OBJECTS TRANSIENT OBJECTS Strict separation of duties Distributed audit trail Limited separation of duties

16 TCEs FOR PERSISTENT OBJECTS open supervisor; {credit clerk + debit clerk}; close supervisor; open Alice; {credit clerk + debit clerk} ; close supervisor; open Alice; {credit clerk + debit clerk} ; close Bob;

17 AUTOMATED TRANSACTION SAGAS 1. A clerk program prepares the voucher and assigns an account 2. The voucher and account are approved by a supervisor program 3.A clerk program issues the check debiting the account as a side effect

18 SUMMARY Transactions Transaction sagas Transaction control expressions (TCEs) Transient versus persistent objects Automated transaction sagas