This schedule is serializable because it can be made equivalent to a serial execution of the transactions, but it is not conflict-serializable nor strictly serial due to the absence of traditional conflicts and strict execution order.
To create a schedule S of transactions that is serializable but not conflict-serializable nor serial, we need to design a scenario where transactions have a dependency that can be resolved by enforcing a particular order, making it serializable but not following the strict rules of conflict-serializability.
Let's create a scenario:
Scenario:
- We have two transactions, T1 and T2.
- Both transactions read and write to the same element X.
- The constants for these transactions are C1 and C2, respectively.
Transactions:
- T1 reads X and writes X as X = X * C1 (e.g., X = X * 5).
- T2 reads X and writes X as X = X * C2 (e.g., X = X * 7).
Schedule S:
- Execute T1, then execute T2.
Step-by-step explanation:
1. T1 reads X and multiplies it by C1, updating X. Let's say X was initially 2, so after T1, X becomes 10 (2 * 5).
2. T2 reads X (which is now 10 after T1) and multiplies it by C2, updating X again. X becomes 70 (10 * 7).
Analysis:
Now, let's analyze the properties of this schedule:
1. Serializable: The schedule is serializable because it can be made equivalent to a serial execution of T1 followed by T2. In the serial execution, X would also become 70 (2 * 5 * 7), which is the same as in schedule S.
2. Not Conflict-Serializable: Schedule S is not conflict-serializable because there is no conflict in the traditional sense (i.e., two transactions trying to access the same data simultaneously). The transactions do not conflict in terms of accessing X at the same time. However, conflict-serializability checks for conflicts based on conflicting operations (read-write, write-read, or write-write), and there is no such conflict here.
3. Not Strictly Serial: Schedule S is not strictly serial because it does not follow a strict order of execution, and the transactions are not isolated from each other. In a strict serial schedule, one transaction would complete before the other begins.