I just wanted to mention that I have doing ASP.NET for about 6 months now and would recommend this book but only after reading the beginner ones. The author assume that you have a good grasp on OOP concepts and experience with the n tier structure.

Back to my question, I was wondering is it really necessary for the BLL to rewrap the data returned from DAL in essentially the same wrapper?

for example: Returning a single Article by ID

- The UI (Show Article.aspx.cs) calls BLL.Article GetArticleByID(ID)

- The BLL calls the DAL.GetArticlesByID which creates an instance of the ArticleDetails object and wraps the data retrieve from the database and exposes the object with ArticleDetails public class members.

- The ArticleDetails object is then used as an argument for the BLL.GetArticleFromArticleDetails method, which then creates and an Article object from it and exposes the object with Article public class members (which are the same members as the DAL). The Article object is then returned to the UI.

Is there a way for the BLL to call the DAL and just pass the object to UI directly without rewrapping it?

There are many possible ways to do it. The objective in a pure n-tier design is to avoid passing a DAL class all the way through to the UI layer. The idea is to hide DAL members from the UI. The DAL interface is a shared-secret only with the BLL.

The question is whether a pure design is always the best design. Sometimes performance issues cause people to make comprimises - I've even seen DataReaders passed from the DAL all the way to the UI. You need to weigh various factors and decide on a combination of design methodologies that you can live with.

I've never seen a real-world system that doesn't break the encapsulation rules at least in some ways. You do realize that in a pure n-tier design you wouldn't be allowed to put ANY functionality in stored procedures, right? Only basic crud is allowable in stored procs using a pure n-tier design because any logic is considered part of the business rules and that is only allowed in the BLL. Both the DAL and DB can only wrap data in a flat manner and do nothing more.

Eric

Thanks... that makes sense to only exposes the UI to the BLL object and not the DAL object.