**Equivalence of Schedules-**

In DBMS, schedules may have the following three different kinds of equivalence relations among them-

- Result Equivalence
- Conflict Equivalence
- View Equivalence

**1. Result Equivalent Schedules-**

- If any two schedules generate the same result after their execution, then they are called as result equivalent schedules.
- This equivalence relation is considered of least significance.
- This is because some schedules might produce same results for some set of values and different results for some other set of values.

**2. Conflict Equivalent Schedules-**

If any two schedules satisfy the following two conditions, then they are called as conflict equivalent schedules-

- The set of transactions present in both the schedules is same.
- The order of pairs of conflicting operations of both the schedules is same.

**3. View Equivalent Schedules-**

We have already discussed about **View Equivalent Schedules**.

**PRACTICE PROBLEMS BASED ON EQUIVALENCE OF SCHEDULES-**

**Problem-01:**

Are the following three schedules result equivalent?

**Solution-**

To check whether the given schedules are result equivalent or not,

- We will consider some arbitrary values of X and Y.
- Then, we will compare the results produced by each schedule.
- Those schedules which produce the same results will be result equivalent.

Let X = 2 and Y = 5.

On substituting these values, the results produced by each schedule are-

**Results by Schedule S1-** X = 21 and Y = 10

**Results by Schedule S2-** X = 21 and Y = 10

**Results by Schedule S3-** X = 11 and Y = 10

- Clearly, the results produced by schedules S1 and S2 are same.
- Thus, we conclude that S1 and S2 are result equivalent schedules.

**Problem-02:**

Are the following two schedules conflict equivalent?

**Solution-**

To check whether the given schedules are conflict equivalent or not,

- We will write their order of pairs of conflicting operations.
- Then, we will compare the order of both the schedules.
- If both the schedules are found to have the same order, then they will be conflict equivalent.

**For schedule S1-**

The required order is-

- R
_{1}(A) , W_{2}(A) - W
_{1}(A) , R_{2}(A) - W
_{1}(A) , W_{2}(A)

**For schedule S2-**

The required order is-

- R
_{1}(A) , W_{2}(A) - W
_{1}(A) , R_{2}(A) - W
_{1}(A) , W_{2}(A)

- Clearly, both the given schedules have the same order.
- Thus, we conclude that S1 and S2 are conflict equivalent schedules.

**Next Article-** **Introduction to Relational Algebra**

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