Issues with Partial Schema usage

[bgs_vb]

Hi,
I have few questions about usage of Partial schemas:

1.)If we define few columns in sequential file column metadata tab and
want to use partial schema file for other set of columns ,can we achieve this using partial schema file concept ?

As my source file is comma delimited and have 3 set of definite columns and other columns may or may not come always .SO i wanted to define first 3 columns in metadata itslef and use partial schema for rest of the column .Plaesea dvis eif it is possible.

2.)As my file is comma delimited and have data as follow:

Joe,LKO,JMathur,Physics,100
Meera,LKO,MMathur,Chemistry,500

In output i want to derive two additional columns using col2 and col5 for calculation as :

Joe,LK,JMathur,Physics,100,LKOCity,1200
Meera,NL,MMathur,Chemistry,500,NLCity,6000

How can i define partial schema file to achieve this .