Business logic tier

here is my problem: My program is an ASP.net�  program. I have a data access layer(DAL) that grab the data and return it as a list of object "List" when I have this list out of database and in�  my server side�  I do apply some other task in my business logic(BLL). for instance my studentBL can calculate Total grad of a student. and also other calss in Bussiness logic mayuse that list to do other calculation. So,in user interface I have a button who do this sequence: �  Instanciate a BLL class Bll class call a DAL to grab data and load the StudentBL with the listso since I have the list ready , I don't want to revisit dataset to get the student data. ( I have it in my webserver in the list).so if the second button in UI will do this: � � �  call the StudentBLL to calculate the grad. � �  StudentBLL already has the student list so can do ithowever, since thi ...