Single Tier—Three Layer Model

In this model, we logically break BL and DAL in different namespaces, introducing cleaner code separation.

ASP.NET Web Project that has logical separation between presentation, business logic and data access code:

Note that it is not necessary to have different folders for the logical separation of code; using different namespaces in different code files will also work fine. We can use this model for a medium-to-large web application where we know that many users won't log in simultaneously. For handling a large number of users, the application needs to be scalable, and to do this we might need to separate BL and DAL code into their own physical assemblies.