timestamp based concurrency
"Transaction T can read or write data item X only if X had not been accessed by a "later" transaction.  Otherwise, the operation of T is rejected; T is aborted and restarted with new TS".

In other words we have:

ST1 and then ST2 any data that is read or write by T2, could not be access by T1 or it will rollback that is because T2 start after T1.

I found it here in the slide 28

I hope it helped you