Subject HowTo: A classic szenario - two reader and two writer

I have an absolutely classical situation:
- two reader browse a data record
- (perhaps) both wonts to change the record
- and at least both write the record back to db.

At the time, both clients read the data record
nobody knows if they also want to change that record.

How do you solve this task correct with FB and Java?
In ORACLE I would not think about this, because
the dbms realize that the second writer has a wrong
"situation" and sends him an exception.

Hans Georg