View Serializability in DBMS

Last Updated on October 18, 2023 by Ankit Kochar

View Serializability in DBMS entails the assessment of whether a provided schedule possesses the quality of being view serializable. A schedule is deemed view serializable if it is equivalent in view to a serial schedule.

Why do We Require View Serializability in DBMS?

Conflict-Serializability encounters limitations when a schedule’s Precedence Graph exhibits a loop or cycle. In such instances, there exist schedules that do not conform to Conflict-Serializability but still yield coherent outcomes. Consequently, the predictability of a schedule’s consistency or inconsistency becomes uncertain. In adherence to the principles of Conflict-Serializability, a schedule attains Conflict-Serializable status only when its associated precedence graph is devoid of any loops or cycles.

Because no concurrent transactions are executed, we know that a serial schedule never leaves the database in an inconsistent state. A non-serial schedule, on the other hand, can leave the database in an inconsistent state because multiple transactions are running concurrently. We ensure that a given non-serial schedule is consistent by ensuring that it is view serializable.

View Equivalent

Let’s see how to determine whether the two schedules are view equivalent.

S1 and S2 are said to view equivalent if they meet the following conditions:

1. Initial Read:
   The initial read of each data item in transactions must match both schedules. For example, if transaction T1 reads data item Y before transaction T2 in schedule S1, then in schedule S2, T1 should read Y before T2.

2. Final Write:
   In both schedules, the final write operations on each data item must match. For example, if a data item Y was last written by Transaction T1 in schedule S1, the last write operation on Y should be performed by Transaction T1 in schedule S2.

3. Update Read:
   If transaction T1 in schedule S1 is reading a data item updated by T2, then in schedule S2, T1 should read the value after T2’s write operation on the same data item. For example, if in schedule S1, T1 performs a read operation on X after T2 performs a write operation on Y, then in schedule S2, T1 should read the Y after T2 performs a write operation on Y.

View Serializable

When a schedule is view equivalent to its serial schedule, it is said to be View Serializable ( view serializability in DBMS).

Let’s understand the concept of the view serializable with the help of the example.

Let’s look at the three view serializability conditions:

1. Initial Read
   First, we will see that transaction T1 in schedule S1 reads data item A first. Transaction T1 in S2 also reads data item A first. Then look for B. Transaction T1 in schedule S1 reads data item B first. T1 also performs the first read operation on B in S2. We checked both data items A and B, and the initial read condition is met in S1 and S2.

2. Update Read
   The second method is about update read operation. Transaction T2 in S1 reads the value of A written by T1. In the same transaction, T2 reads the A after it is written by T1 in S2. Transaction T2 in S1 reads the value of B written by T1. The same transaction T2 reads the value of B after it has been updated by T1 in S2. Both schedules also satisfy the update read condition.

3. Final Write
   In schedule S1, the final write operation on A is done by transaction T2. Transaction T2 also performs the final write on A in S2. Let’s look for B. Transaction T2 performs the final write operation on B in schedule S1. T2 completes the final write on B in schedule S2. We checked both data items A and B, and the final write condition is met in S1 and S2.

Conclusion
View Serializability in DBMS is a fundamental concept in Database Management Systems (DBMS) that deals with the scheduling of transactions to ensure that the final state of the database remains consistent and predictable. It assesses whether a given schedule is equivalent in view to a serial schedule. This concept becomes particularly relevant when considering schedules that may not conform to Conflict-Serializability due to the presence of cycles in their Precedence Graphs.

FAQs Related to View Serializability in DBMS

Here are some of the FAQs related to View Serializability in DBMS:

1. What is the importance of View Serializability in DBMS?
View Serializability ensures that the final state of the database remains consistent and predictable, regardless of the order in which transactions are executed. It helps maintain data integrity in a multi-user database environment.

2. How is View Serializability different from Conflict-Serializability?
Conflict-Serializability primarily considers conflicts between read and write operations in transactions. View Serializability, on the other hand, looks at whether the outcome of a schedule is equivalent to that of a serial schedule, regardless of conflicts.

3. What is a Precedence Graph in the context of View Serializability?
A Precedence Graph is a graphical representation used to analyze the dependencies between transactions in a schedule. It helps determine whether a schedule is View Serializable by examining if there are cycles in the graph.

4. Why is View Serializability important for database design and management?
View Serializability is essential because it ensures that database transactions can be executed in a way that maintains data consistency and integrity, even in a multi-user environment where multiple transactions are occurring simultaneously.