THE QUESTION IS ABOUT THE SUBJECT DATABASE! PLEASE ANSWER STEP BY STEP AND NOT THROUGH EXCEL OR ANY OTHER PROGRAMS PLEASE! THANKS!

Question 3: Transactions a) When several transactions are executed simultaneously, it is important that they do not affect each other. Having no control mechanism is one of the problems that can arise the lost update problem. Explain how this problem manifests itself. b) Draw a precedent graph for the diagram below where all conflicts are plotted. Available it an equivalent serial schedule? If yes, what can it look like? c) 2PL (two-phase locking) is a technology for concurrency control. How does it work and why is it so important? d) Describe in detail by example how a database can recover after one system crash, in a system that uses immediate update. 

T2 T3 read_item (X); write_item (X); read_item(Y); read item(2); read_item(Y); write_item(Y); read_item(Y); write_item(Y); write_item(Y); write_item(2); read_item(2); read_item (X); write_item (X)