well, what I make sense to me is how can an employee work on mutiple work, definately human cannot focus on two task at the same time and there will be stop / start time for switching with jobs, but as I asked what kind of job is it? and what is company doing? how do you measure that employee work or not? and how do you detect which job he's up to? is it based on computer login system?

if you want to determine working time of users you have to keep track of what he didn't do or his free times. lets say I am an employee and this is my working timeline

you have to do some categorization for your tables , Sessions, Task, check in, check out, working time.

SessionID = 1

Date 1/1/2004
check in = 8:00 am <<< When I come to company

TaskID = 1
Job Name = Duty A
Start=8:00am
End= 1:00pm

TaskID = 2
Job Name = Duty B
start=10:00 am
end=2:00 pm

CheckOUT = 6:00 pm << When I left company


well I haven't work from 2:00 pm until 6:00 pm so it will be 4 hours and my check-in was 8:00 means I was online for 10 hours and I was only working for 6 hours and for 3 hours I had been working on two project and for 3 hours I was working on one task only...

is it what you want ?

Hope I could be any help
S. Mohammad Najafi

PS : more description, better result for your answer