Re: only allows access to one customers record at a time
Database system are designed to be as fast as possible, not to impose delays. You need to understand that there is not just one terminal (aka PC) making requests to the database, there are hundreds, if not thousands. You have the hostesses in the airports, registering luggage, you have travel agents querying the best way for their customer to travel, you have people on the Internet looking it up for themselves, and there is probably a bunch of other possible ways to send demands that I haven't the foggiest idea of.
If you create a system where only one request can be served at a time, you are basically choking the whole system beyond usability and the whole thing collapses.