In this chapter students will be able to: Explain the primary difference between the traditional technology approach and the object-oriented technology approach, list and describe the five primary object-oriented concepts, explain how classes and objects are related, discuss the three fundamental principles of object-oriented technologies, describe two types of object-oriented technologies. | Lecture 28 Enterprise Systems Development ( CSC447) COMSATS Islamabad Muhammad Usman, Assistant Professor College of Statistical and Acturial Science Schedules Schedule – a sequences of instructions that specify the chronological order in which instructions of concurrent transactions are executed a schedule for a set of transactions must consist of all instructions of those transactions must preserve the order in which the instructions appear in each individual transaction. A transaction that successfully completes its execution will have a commit instructions as the last statement by default transaction assumed to execute commit instruction as its last step A transaction that fails to successfully complete its execution will have an abort instruction as the last statement Schedule 1 Let T1 transfer $50 from A to B, and T2 transfer 10% of the balance from A to B. A serial schedule in which T1 is followed by T2 : Schedule 2 A serial schedule where T2 is followed by T1 Schedule 3 Let T1 and T2 be the transactions defined previously. The following schedule is not a serial schedule, but it is equivalent to Schedule 1. In Schedules 1, 2 and 3, the sum A + B is preserved. Schedule 4 The following concurrent schedule does not preserve the value of (A + B ). Serializability Basic Assumption – Each transaction preserves database consistency. Thus serial execution of a set of transactions preserves database consistency. A (possibly concurrent) schedule is serializable if it is equivalent to a serial schedule. Different forms of schedule equivalence give rise to the notions of: 1. conflict serializability 2. view serializability Simplified view of transactions We ignore operations other than read and write instructions We assume that transactions may perform arbitrary computations on data in local buffers in between reads and writes. Our simplified schedules consist of only read and write instructions. Conflicting Instructions Instructions li and | Lecture 28 Enterprise Systems Development ( CSC447) COMSATS Islamabad Muhammad Usman, Assistant Professor College of Statistical and Acturial Science Schedules Schedule – a sequences of instructions that specify the chronological order in which instructions of concurrent transactions are executed a schedule for a set of transactions must consist of all instructions of those transactions must preserve the order in which the instructions appear in each individual transaction. A transaction that successfully completes its execution will have a commit instructions as the last statement by default transaction assumed to execute commit instruction as its last step A transaction that fails to successfully complete its execution will have an abort instruction as the last statement Schedule 1 Let T1 transfer $50 from A to B, and T2 transfer 10% of the balance from A to B. A serial schedule in which T1 is followed by T2 : Schedule 2 A serial schedule where T2 is followed by T1
