Employee Substitution-Shift

Hi,

How to configure the shift substitution of an employee.

My client has 3 shifts i.e A, B, C. Some times employee ( Mr. X)  skips the A shift or comes in second  shift.

Now the requirement is,

a. when employee skips the shift , how to substitute the person form other dept.( Mr.Y)

b. what changes required to configure.

c. what happens when Mr.X comes in second shift.

d. what are the requirements need to be considered for Mr.Y.( Extra Pay or Comp off- )- for this client if employee works more that 3 hours he need pay some allowance.

e. how to configure these requirements.

I have very little knowledge on info type 2003.

Kindly guide me.

Regards,

Sumana