What is the use of a persistence layer in any application?

Question

I have to create an application in which I am asked to create an persistence layer in the application. The application is in .net. I have created a business layer and a pres

Answer 1

If you're not saving your data somewhere, it won't be there again when your app is opened again. You can save it to a database as you said (SQL, Oracle, PostGRE etc.), or directly to disk (serializing in binary format, or plain text etc.).

Using a layer to do that is a good practice. It reduces coupling (i.e. spaghetti code), and makes maintenance much easier.

I suggest you read about Hibernate and it's .NET cousin, NHibernate.