I have a begginers design issue.
I'm building an layered application(Presentation layer, Business logic layer and Data base layer).
I have three entities in my application:customer,staff member and vendor that all of them deriving from person.
The user can add new customer,staff member or vendor to the data base(using UI).
My question is which layer is responsible for the next tasks:
1.Validating user data
2.Saving customer,staff member,vendor in to the DB.
3.Retrieving customer,staff member,vendor from the DB.
4.Perform other DB related manipulation with customer,staff member,vendor.
5.Which classes i need to define to perform the above tasks.
I'm new in to object oriented programming so thru the current question i am trying to understand the concept.