Please let me know if it is wrong. Or any other simple to solve.

Transcation{
private Transcation prev;
private HashMap<String, Integer> name_value = new HashMap<String, Integer>();

}
class Database {
private LinkedList blocks;
public boolean commit() // create new block;
rollBack // remove tail;
begin() // add new block
get()// fetch it from trail. which will be latest
set()// set value to current node.

}