Database Theory: Transaction serializability

Question

Hy, I'm learning for my exams and came over the following question:

Take the History (or Schedule)

H = w1[x] w2[x] w2[y] c2 w1[y] w3[x] w3[y] c3 w1[z] c1

where w1[x] means: Transaction 1 writes to Data-Object X (r1[x] means read) and c1 means: Transaction 1 commits.

Why is this transaction view serializable?

For view Serializability the History H must be view-equivalent to a sequential executing of the transaction 1,2,3. So, futher, the last-writes of each data-Object must be the same as in a sequential execution of the transaction of the History H. So the last-Writes of H are:

• Transation 3 for x and y and
• Transation 1 for z

But, in no sequential execution the last-writes are distributed like this, so the History H can't be view serializable.

Where is my mistake?

Thanks everyone.

Answer 1

Okay, found out myself: The last sentence if of course wrong:

In fact the sequential execution 1,2,3 leads to this History:

w1[x] w1[y] w1[z] c1   w2[x] w2[y] c2    w3[x] w3[y] c3

and the follogint last-Writes:

• Transaction 3 for x and y and
• Transaction 1 for z

which is the same than the last-writes of History H