Displaying the mean and variance of purchased items

Hi

i am trying to create a program using WML, WMLSCRIPT, AND JSP. The task is to create a website to be displayed in the WAP Browser. In the website for a company called 'BargainBook' that sells books and the ERD diagram for this is attached as picture (see attachement).

So now I have just finished creating a login and register page and nearly done on purchase page BUT what I want to do is to find out how to display the MEAN and VARIANCE of purchased books in a given period of time (let say 1 week for example) . Plus how can I extend my ER Diagram in order to add this because I think I may need a separate entity (or table) for this.

Any explanation will be very much appreciated. As I said I think need a new table for this BUT I do not know what kind of record should be stored on it that would help with the calculation. And also, I would like to know the suitable SQL queries to calculate the mean and variance for a given period of time.



thanks

re: Displaying the mean and variance of purchased items

Sorery Here Is The Attachment

Attached Images

er_bookshop_4.jpg (27.4 KB, 200 views)

re: Displaying the mean and variance of purchased items

Hi,

Sorry I have no suggestions. I am posting this msg to get ideas from regarding this project. I am developing a project based on m-commerce security and i am using nokia 6600, java, wml. Could u share ur ideas on this project...my mail address is rejoice_cb@yahoo.com...

Thank u,