Question

I think BLL is about Data. It should not include a method called SendEmail. BLL is a place for caching data, manipulating it, doing calculations related to business. Sending email is a business process but the code which actually send the email should be outside of BLL namespace.

Is BLL only about data ?

Answer 1

BLL is not about data, It is all about what needs to be done with the
data.

• User will only interact with the front-end presentation-forms of any application, which is popularly known as presentation layer.

• Data will be displayed or exchanged as input/output to this layer from various sources of data. These sources are databases or web-services. The piece of code that actually fetches or sends these data to respective sources of data is what we call as DAL – data access layer.

• In between the application does special operations which we call application-requirements or user-needs. This strategic part of the application is called BLL that actually addresses needs of the client for which you are developing the application.

• If data needs to be stored in the database, BLL will have DAL as an underlying layer.

• BLL is not aware of the sources of data and how data is fetched or sent to data-sources. You have DAL for that. BLL only knows about data, that to in forms of business-objects more often and operations on the data business-objects.

• BLL also does not know whether user is using website or a desktop application. You have presentation layer for that.